History ObviousRulePatch / Pokemon

* Yellow version, which is premised on being a RecursiveAdaptation of the anime and thus gives you Pikachu and only Pikachu as your starter, rewired the appearance distribution and movelists of some early Pokémon to prevent Brock from being an overly-frustrating EarlyBirdBoss, since his Pokémon are all part Ground-type. Mankey becomes available west of Viridian City, both Nidoran learn Double Kick at level 9, and Butterfree learns Confusion at level 10, immediately upon evolving.

* With the introduction of the gender and [[CreatureBreedingMechanic breeding]] mechanics, in order to prevent people from breeding a bunch of starters, all of them have 7:1 male-to-female ratio. However, as TechnologyMarchesOn, this effort was largely made obsolete by features such as Wonder Trade that allows people to obtain starters with relative ease, but the tradition persists to this day, leading to some awkwardness as starters with feminine designs like Delphox and Primarina [[DudeLooksLikeALady being almost entirely male]]. Not to mention the fact that it was pointless to begin with, as they put Ditto ''right outside the Daycare and third gym'' in Gen II.
* Psychic-types in Generation I were very broken. Nothing resisted Psychic moves except Psychic itself, and its intended weaknesses, Bug and Ghost, suffered from underpowered moves and weak rosters, as well as a programming error that made Ghost completely ineffective on Psychics. When Generation II rolled around, the developers added two new types to act as counters: Dark did super-effective damage against Psychic while being [[NoSell completely immune]] to Psychic moves in return, while Steel simply resisted Psychic moves.[[note]]These types were not created ''solely'' to counter Psychic, but that was arguably their biggest impact.[[/note]] Meanwhile, Ghost moves became properly effective against Psychic as intended, and both Ghost and Bug got stronger moves and more capable Pokémon.
* Unlike physical moves, special moves used the same stat for both attacking and defending. This meant that while an individual Pokémon could be good at using physical moves but bad at defending against them or vice versa, being good at using special moves automatically made a Pokémon good at defending against them. Add in the move Amnesia, which boosted the Special stat by two stages, and a Special-oriented Pokémon could quickly become a nightmare to take down. To make matters worse, at this point in the series, a move's type was what determined whether it was physical or special, and Psychic was one of the special types; see above for why this was such a bad thing. Generation II wisely split the Special stat into Special Attack and Special Defense, putting physical and special moves on more even footing, and later generations would determine which moves used which offensive stat (ie Physical Attack or Special Attack) on a move-by-move basis, and not base it on the type of the attack. For example, the elemental punches were all considered physical attacks in later generations. Amnesia's boost now only applies to Special Defense, while Nasty Plot was introduced to cover Special Attack, and Calm Mind was introduced later as a weaker combination.
* There are several moves that protect the user from taking damage that turn, most commonly Protect. Attempting to use Protect multiple turns in a row sharply slices its success rate to prevent indefinite stalling. Furthermore, similar guarding moves like Detect, Endure, and Spiky Shield all use the same mechanic, so you can't just alternate between multiple such moves to avoid the success rate reduction.
* Critical hits and instant-KO moves were both dependent on the user's Speed stat, to the point where faster Pokémon were almost guaranteed to crit. Furthermore, multi-hit moves would always crit on every hit or none per use. Generation II made the critical hit rate dependent on the move used instead and had multi-hit moves calculate crit chance independently for each hit, while instant-KO moves changed to depend on the level difference between the user and the target. That said, it wasn't a total loss for critical hits, since Gen II also fixed several bugs regarding critical hit chance and allowed critical hits to benefit from stat boosts during damage calculations.
* Hyper Beam had a number of ways to bypass the cooldown turn after use, such as if it misses, the target faints, or it broke a Substitute. Come Generation II, all of these loopholes have been closed (except for missing) to give the move more of a downside.
* Certain ongoing-damage moves such as Wrap would trap the target, rendering them completely unable to act for the duration. As of Generation II, the target still gets to attack; such moves now deal damage every turn without restricting a target's speed or ability to act (though they ''do'' now prevent switching).
* Struggle, the unique move reserved for when a Pokémon runs out of PP, behaved as a Normal move, which made it completely unable to affect Ghost-types. Later games would have it behave as a "typeless" move instead.

* In its original appearance in ''VideoGame/PokemonRubyAndSapphire'', the Pickup ability was a classic DiscOneNuke. Since it's available on a ComMon that pretty much everyone catches immediately and it has the chance of acquiring excellent items that players typically have to grind for (including, most famously, [[RareCandy Rare Candies]]), it takes practically no effort to grind out an item trove that allows a player to roll over most of the game. In ''Emerald'' onwards, the list of possible finds was dependent on the level of the Pickup user -- it still had the potential for some of the best items in the game, but a Pickup user had to be higher level to get them, and the lower levels still would garner some useful but not overpowered ones.
* A Pokémon designed after punching bags, Wobbuffet cannot attack directly but must return an opponent's damage with interest. However, when debuted in Generation II, Wobbuffet could not stop the opponent from just switching out over and over while it burned all of its PP. When Generation III introduced Abilities, Wobbuffet and its new baby form Wynaut got Shadow Tag, which prevents the opponent from switching out, to compensate. Unfortunately, in competitive matches, you could easily end up in a draw if two Wobbuffets with Leftovers ended up facing off, as neither could switch out or do enough damage to knock the other out. Generation IV quickly adjusted Shadow Tag so that it also granted immunity against its own effect, and the self-damage calculation for Struggle got altered to make it depend on the user's maximum health rather than the damage dealt to the target.
* Shedinja, a Bug/Ghost type Pokémon, has permanent OneHitPointWonder to counter its NoSell ability, Wonder Guard. This blocks it from taking any direct damage that does not hit it super effectively, though it is still vulnerable to damage over time effects, damaging weather, abilities, and items. Since it has ''five'' weaknesses, it's also pretty easy to counter on that front, leaving it basically unusable apart from a few gimmicks like hard countering Kyogre. However, wouldn't it be nice if you could drop Wonder Guard onto, say, Sableye? Which until Generation VI[[note]]Said Generation introduced the Fairy type, which is strong against Dark, while Ghost cannot resist it.[[/note]] had no weaknesses at all? Nope! Banned! Can't be done, as moves like [[PowerCopying Role Play and Skill Swap]] are programmed to fail if used on this ability. The only way to get Wonder Guard onto another Pokémon is via Trace, or having Shedinja use Mimic to copy the move Entrainment, the former being only possible for your opponent and the second only being usable in Double Battles and [[AwesomeButImpractical requiring significant setup that can easily be stopped]].

* In this generation, there was a glitch involving the new move Sky Drop. The move makes one Pokémon take another into the air (and then drop it for damage), and when a Pokémon is in the air, it cannot move or be hit (except by a few moves, like Thunder). There was previously a move called Gravity which made Flying-types or levitating Pokémon come to the ground (this meaning they can be hit by Ground-type moves). In a double battle, if one of your Pokémon uses Sky Drop and the other then uses Gravity, both Pokémon will come to the ground... [[GameBreakingBug except while your Pokémon can move, theirs is treated as being in the air and cannot move, at all, until they are fainted by a move like, say, Thunder]]. The Obvious Rule Patch? Nintendo banned Sky Drop in random online battles.

* Just as Generation II brought in Dark and Steel to tame Psychic, Generation VI introduced the new Fairy type to revise imbalances in the type chart. This time around, Fairy had four existing types to tweak. Dragon and Fighting had run roughshod over the meta during Generation V, so they both took extra damage from Fairy while dealing less to it (or none, in Dragon's case); same with Dark, presumably because the Pokémon which most needed to be {{Nerf}}ed, Hydreigon, is a Dark/Dragon dual type. Meanwhile, Steel and Poison had previously been regarded as poor offensive options, so Fairy's weaknesses to them gave them a new niche.
* The introduction of non-legendary Pokémon with the abilities Drought, Drizzle, Snow Warning, and Sandstream (which would set up sunny, rainy, hail/snowy, or sandstorm weather respectively) in Generation V led to the so-called Weather Wars, in which the competitions (both in Smogon and Nintendo-sanctioned tournaments) stagnated around setting up the player's preferred type of weather (generally by simply sending out something with the appropriate ability) and using a team built around getting buffs from said weather (most famously, Swift Swim teams built around Drizzle Politoed). Generation VI finally brought balance by making weather-inducing abilities function the same as the moves that induced weather and giving them a 5-turn limit (with a held item extending it up to eight turns).
* Pokémon with Oblivious as an Ability are immune to Infatuation, a status almost never used in any serious competition. This generation makes the Ability block an oft-used status move Taunt (which prevents the use of status moves), essentially repurposing an Ability for an entirely different purpose (but one still marginally related to [[CaptainOblivious obliviousness]]). As of Generation VIII onwards, the Ability also blocks Intimidate, an oft-used Ability that lowers physical Attack upon entering the field.
* In Generations IV and V, there were problems with [[RageQuit players disconnecting to preserve their win-loss record]]. In ''VideoGame/PokemonXAndY'', however, disconnecting on players will count as a loss to the player who shut their game off.

** The games have [[DevelopersForesight gone out of their way]] to ensure a Mega-Evolved Pokémon can't use a Z-Move under any circumstances. Example; if a Pokémon holding a Z-Crystal uses Transform or the Imposter ability to transform into a Mega Pokémon, if it tries to use a Z-Move, it'll say that there's no compatible move, even if it knows a move of a matching type.
* Dark Void is a very powerful move in Double Battles (putting both opposing Pokémon to sleep), normally mitigated by it being exclusive to [[OlympusMons Darkrai]], a Pokémon normally banned in competitions. However, Smeargle can learn any move in the game through Sketch, and as a result Dark Void Smeargle ran rampant through the Video Game Championships scene for years, annoying players to no end due to how difficult it was to counter. ''VideoGame/PokemonSunAndMoon'' not only [[{{Nerf}} Nerfed Dark Void's accuracy to 50%]], but made it ''automatically fail if used by any Pokémon other than Darkrai''.

* Intimidate is an Ability that reduces the opposing Pokémon's Attack that sees huge competitive use due to its immediate effect upon entering the field. In this generation, several Abilities[[note]]Oblivious, Own Tempo, Inner Focus, and Scrappy.[[/note]] are buffed to block Intimidate in addition to their original effects and Rattled[[note]]Increases speed when hit by a damaging Bug, Dark, or Ghost move.[[/note]] is buffed to also be triggered by Intimidate.
** Guard Dog, an ability introduced in Generation IX, raises the user's Attack instead of lowering when Intimidated (in addition to being immune to being forced to switch out).
* Mimikyu's Disguise Ability meant that it completely shrugs off one attack per battle until it faints, regardless of power. This means that giving it the Focus Sash at full HP will allow it to survive at least two hits that would have knocked it out. In this generation afterwards, Mimikyu loses 1/8 of its max HP upon tanking the damage with Disguise to reduce its synergy with Focus Sash.
* Abilities that [[GeoEffects automatically generate terrain when the Pokémon is brought in]] -- Grassy Surge, Misty Surge, Psychic Surge, and Electric Surge -- were introduced in Generation VII's ''VideoGame/PokemonSunAndMoon''. Among other effects, most of them granted a 50% boost in damage to their corresponding types, like Grass with Grassy Terrain. At the time, only the Alolan Island Guardians could have these Abilities, and that boost caused them to have such immense damaging power that they could not only plow through in-game challenges, but they could be found on most people's competitive teams in all battling modes. ''VideoGame/PokemonSwordAndShield'' onwards reduces the terrain's damage boost to 30%. Its "Isle of Armor" DLC campaign also added in the move Steel Roller, a very high-damage Steel-type attack that removes any terrain in the battle. All of the Island Guardians are part-Fairy, which is weak to Steel-type attacks.

* [[WhenAllYouHaveIsAHammer Adaptability]] is an Ability that was introduced all the way back in Gen IV and increases the STAB multiplier from 1.5x to 2x for moves of the same type as the user. Terastallization is also a mechanic that does the same if the user Terastallizes into (one of) its same type(s). Should you attempt to Terastallize a Pokémon with Adaptability (e.g. Tera Water Crawdaunt), instead of both multipliers stacking, the resulting boost is 2.25x instead, [[AvertedTrope preventing such mons]] from [[ThereIsNoKillLikeOverkill becoming obscenely powerful wallbreakers]].

* ''VideoGame/PokemonBlackAndWhite'' gave Politoed the ability to make permanent rain, which gives numerous bonuses to certain Pokémon (including increasing the power of water type moves and activating certain abilities). One of these abilities, Swift Swim, doubled the Pokémon's speed under rain. At the beginning of Black and White, Politoed plus Swift Swim sweepers ran wild over the game. Smogon came up with a complex ban. Politoed could not be on a team with a Swift Swim Pokémon.
* Smogon tier lists are usually determined by usage. The more a Pokémon is used, the higher the tier it is in, the logic being that players will use the better more often. However, there were Pokémon that were not used enough to be useful in a higher tier but came to utterly dominate some lower tier. For example, in Black and White, no one would use Kyurem in Overused, but it completely destroyed most Pokémon in Underused. Smogon created "borderline" (now called ban lists) for Pokémon that are too good to be used in one tier but not used enough to be placed into a higher tier.
* Originally, tier lists were determined only by usage. After a user named "ihabt" decided to use several Neverused Pokémon in Rarelyused with terrible movesets and setups frequently with the intent of moving them up to Rarelyused, Smogon changed things so that such a Pokémon can't just be used in a specific tier, it needs to be viable and capable of winning enough battles in that tier as well.

* Some Nuzlocke runs of later generations will have additional rules to account for new mechanics not present in Generation 3, where the ''Webcomic/NuzlockeComics'' originated. For example, ''VideoGame/PokemonOmegaRubyAndAlphaSapphire'' introduced the [=DexNav=] and sneaking through grass, which would make the Nuzlocke rule of "You can only catch the first encounter on a route" a complete joke since getting a really good first encounter would be incredibly easy. Possible rule patches for this would be to either forbid using the [=DexNav=] entirely, forbid sneaking through grass to get to a detected Pokémon until you're right next to it, or consider the first detected Pokémon the first encounter (so if it's not ideal, too bad, and if you give it up, you can't try again).

* Unlike physical moves, special moves used the same stat for both attacking and defending. This meant that while an individual Pokémon could be good at using physical moves but bad at defending against them or vice versa, being good at using special moves automatically made a Pokémon good at defending against them. Add in the move Amnesia, which boosted the Special stat by two stages, and a Special-oriented Pokémon could quickly become a nightmare to take down. To make matters worse, at this point in the series, a move's type was what determined whether it was physical or special, and Psychic was one of the special types; see above for why this was such a bad thing. Generation II wisely split the Special stat into Special Attack and Special Defense, putting physical and special moves on more even footing, and later generations would determine which moves used which offensive stat (ie Physical Attack or Special Attack) on a move-by-move basis, and not base it on the type of the attack. For example, the elemental punches were all considered physical attacks in later generations.

* With the introduction of the gender and [[CreatureBreedingMechanic breeding]] mechanics, in order to prevent people from breeding a bunch of starters, all of them have 9:1 male-to-female ratio. However, as TechnologyMarchesOn, this effort was largely made obsolete by features such as Wonder Trade that allows people to obtain starters with relative ease, but the tradition persists to this day, leading to some awkwardness as starters with feminine designs like Delphox and Primarina [[DudeLooksLikeALady being almost entirely male]]. Not to mention the fact that it was pointless to begin with, as they put Ditto ''right outside the Daycare and third gym'' in Gen II.

* Yellow version, which is premised on being a RecursiveAdaptation of the anime and thus gives you Pikachu and only Pikachu as your starter, rewired the appearance distribution and movelists of some early Pokémon to prevent Brock from being a WakeUpCallBoss, whose Pokémon are all part Ground-type. Mankey becomes available west of Viridian City, both Nidoran learn Double Kick at level 9, and Butterfree learns Confusion at level 10, immediately upon evolving.

* With the introduction of the gender and [[CreatureBreedingMechanic breeding]] mechanics, in order to prevent people from breeding a bunch of starters all of them have 9:1 male-to-female ratio. However, as TechnologyMarchesOn this effort was largely made obsolete by features such as Wonder Trade that allows people to obtain starters with relative ease, but the tradition persists to this day leading to some awkwardness as starters with feminine designs like Delphox and Primarina [[DudeLooksLikeALady being almost entirely male]]. Not to mention the fact that it was pointless to begin with as they put Ditto ''right outside the Daycare and third gym'' in Gen II.
* Psychic-types in Generation I were very broken. Nothing resisted Psychic moves except Psychic itself, and its intended weaknesses, Bug and Ghost, suffered from underpowered moves and weak rosters, as well as a programming error that made Ghost completely ineffective on Psychics. When Generation II rolled around, the developers added two new types to act as counters: Dark did super-effective damage against Psychic while being [[NoSell completely immune]] to Psychic moves in return, while Steel simply resisted Psychic moves.[[note]] These types were not created ''solely'' to counter Psychic, but that was arguably their biggest impact.[[/note]] Meanwhile, Ghost moves became properly effective against Psychic as intended, and both Ghost and Bug got stronger moves and more capable Pokémon.

* Hyper Beam had a number of ways to bypass the cooldown turn after use, such as if it misses, the target faints, or it broke a Substitute. Come Generation II, all of these loopholes have been closed to give the move more of a downside.
* Certain ongoing-damage moves such as Wrap would trap the target, rendering them completely unable to act for the duration. As of Generation II, the target still gets to attack; such moves now deal damage every turn without restricting a target's speed or ability to act.

* Shedinja, a Bug/Ghost type Pokémon, has permanent OneHitPointWonder to counter its NoSell ability, Wonder Guard. This blocks it from taking any direct damage that does not hit it super effectively, though it is still vulnerable to damage over time effects, damaging weather, abilities and items. Since it has ''five'' weaknesses, it's also pretty easy to counter on that front, leaving it basically unusable apart from a few gimmicks like hard countering Kyogre. However, wouldn't it be nice if you could drop Wonder Guard onto, say, Sableye? Which until Generation VI[[note]]Said Generation introduced the Fairy type, which is strong against Dark, while Ghost cannot resist it.[[/note]] had no weaknesses at all? Nope! Banned! Can't be done, as moves like [[PowerCopying Role Play and Skill Swap]] are programmed to fail if used on this ability. The only way to get Wonder Guard onto another Pokémon is via Trace, or having Shedinja use Mimic to copy the move Entrainment, the former being only possible for your opponent and the second only being usable in Double Battles and [[AwesomeButImpractical requiring significant setup that can easily be stopped]].

* In this generation, there was a glitch involving the new move Sky Drop. The move makes one Pokémon take another into the air (and then drop it for damage), and when a Pokémon is in the air, it cannot move or be hit (except by a few moves, like Thunder). There was previously a move called Gravity which made Flying-types or levitating Pokémon come to the ground (this meaning they can be hit by Ground-type moves). In a double battle, if one of your Pokémon uses Sky Drop and the other then uses Gravity, both Pokémon will come to the ground... [[GameBreakingBug except while your Pokémon can move, theirs is treated as being in the air and cannot move, at all, until they are fainted by a move like, say, Thunder.]] The Obvious Rule Patch? Nintendo banned Sky Drop in random online battles.

* The introduction of non-legendary Pokémon with the abilities Drought, Drizzle, Snow Warning, and Sandstream (which would set up sunny, rainy, hail/snowy, or sandstorm weather respectively) in Generation IV led to the so-called Weather Wars, in which the competitions (both in Smogon and Nintendo-sanctioned tournaments) stagnated around setting up the player's preferred type of weather (generally by simply sending out something with the appropriate ability) and using a team built around getting buffs from said weather (most famously, Swift Swim teams built around Drizzle Politoed). Generation VI finally brought balance by making weather-inducing abilities function the same as the moves that induced weather and giving them a 5-turn limit (with a held item extending it up to eight turns).

* In Generations IV and V, there were problems with [[RageQuit players disconnecting to preserve their win-loss record.]] In ''VideoGame/PokemonXAndY'', however, disconnecting on players will count as a loss to the player who shut their game off.

** The games have [[DevelopersForesight gone out of their way]] to ensure a Mega-Evolved Pokémon can't use a Z-Move under any circumstances. Example; if a Pokémon holding a Z-Crystal uses Transform or the Imposter ability to transform into a Mega Pokémon, if it tries to use a Z-Move it'll say that there's no compatible move even if it knows a move of a matching type.

* Starting from the ''[[VideoGame/PokemonLetsGoPikachuAndEevee Let's Go Pikachu and Eevee]]'', Pokémon Storage System can be accessed at any time, instead of needing to return to a Pokémon Center. Accordingly, Pokémon deposited into a Box will not be automatically healed (as was the case in previous generations except in Gen I).

* Abilities that [[GeoEffects automatically generate terrain when the Pokémon is brought in]]--Grassy Surge, Misty Surge, Psychic Surge, and Electric Surge--were introduced in Generation VII's ''VideoGame/PokemonSunAndMoon''. Among other effects, most of them they granted a 50% boost in damage to their corresponding types, like Grass with Grassy Terrain. At the time, only the Alolan Island Guardians could have these Abilities, and that boost caused them to have such immense damaging power that they could not only plow through in-game challenges, but they could be found on most people's competitive teams in all battling modes. ''VideoGame/PokemonSwordAndShield'' onwards reduces the terrain's damage boost to 30%. Its "Isle of Armor" DLC campaign also added in the move Steel Roller, a very high-damage Steel-type attack that removes any terrain in the battle. All of the Island Guardians are part-Fairy, which is weak to Steel-type attacks.

* The Endless Battle Clause itself had to be modified several times to account for [[{{Troll}} certain creative types]] finding ways around the convoluted ban, which at its core involved a Leppa Berry [[note]][[ManaPotion Restores 10 PP to any move that runs out of PP]][[/note]], the move Recycle [[note]]Recovers a used item, such as a Leppa Berry; in this case allowing infinite PP restoration[[/note]], and some method of keeping the opponent from suiciding from Struggle recoil, of which there are shockingly many methods.

* Originally, tier lists were determined only by usage. After a user named "ihabt" decided to use several Neverused Pokémon in Rarelyused with terrible movesets and setups frequently with the intent of moving them up to Rarelyused, Smogon changed things to that such a Pokémon can't just be used in a specific tier, it needs to be viable and capable of winning enough battles in that tier as well.

* While a player can have both a Dusk Mane Necrozma and a Dawn Wings Necrozma in their party in ''VideoGame/PokemonUltraSunAndUltraMoon'', only one of them can transform into Ultra Necrozma per battle; transforming one will prevent the other from doing so, even if the transformed Necrozma faints.

''Franchise/{{Pokemon}}'' has been subject to a few {{Obvious Rule Patch}}es:

* The UsefulNotes/VirtualConsole release of ''VideoGame/PokemonRedAndBlue'' does not allow Save States (a standard feature for other Virtual Console games released on the UsefulNotes/Nintendo3DS) to prevent players from cloning Pokémon, and prevents players from transferring [[OlympusMons Mew]] obtained through a glitch. In addition, all Pokémon transferred have their Hidden Abilities, otherwise people could use an Ability Capsule on Machamp to give it No Guard to ensure [[OneHitKill Fissure]] (which the TM for only existed in Gen I) would always land.

* [[invoked]] Yellow version, which is premised on being a RecursiveAdaptation of the anime and thus gives you Pikachu and only Pikachu as your starter, rewired the appearance distribution and movelists of some early Pokémon to mitigate the natural DifficultySpike given to Brock, whose Pokémon are all part Ground-type. Mankey becomes available west of Viridian City, both Nidoran learn Double Kick at level nine, and Butterfree learns Confusion at level ten, immediately upon evolving.

!!Generation XI

!!Unsorted
* This is the purpose of the obedience mechanic. Once you unlock trading, there's really nothing stopping you from getting a high-level Pokémon from a friend. The obedience mechanic is designed to prevent you from using traded Pokémon to crush the game under your heel by making it so high-leveled Pokémon acquired from other Trainers have a very high chance of not listening to your commands until you collect the proper amount of Gym Badges (or Trials, in the case of Generation VII). In ''Sword and Shield'', this mechanic was extended to the ability to ''catch'' high-level Pokémon outside of Raids due to the presence of the Wild Area where you can meet high-level wild Pokémon early. In ''Legends: Arceus'' onwards, the catch penalty was mostly removed and obedience was changed so that it is based on the level the Pokémon is caught/traded at rather than its current level, preventing legitimate outsider Pokémon from going disobedient when overleveled.
* Generation II introduced the gender and [[CreatureBreedingMechanic breeding]] mechanics, and in order to prevent people from breeding a bunch of starters they made all of them nearly 90% male. However, as TechnologyMarchesOn this effort was largely made obsolete by features such as Wonder Trade that allows people to obtain starters with relative ease, but the tradition persists to this day leading to some awkwardness as starters with objectively feminine designs like Delphox and Primarina [[DudeLooksLikeALady being almost entirely male]]. Not to mention the fact that it was pointless to begin with as they put Ditto ''right outside the Daycare and third gym'' in Gen II.
* Just as Generation II brought in Dark and Steel to tame Psychic, Generation VI introduced the new Fairy type to revise imbalances in the type chart. This time around, Fairy had four existing types to tweak. Dragon and Fighting had run roughshod over the meta during Generation V, so they both took extra damage from Fairy while dealing less to it (or none, in Dragon's case); same with Dark, presumably because the Pokémon which most needed to be {{Nerf}}ed, Hydreigon, is a Dark/Dragon dual type. Meanwhile, Steel and Poison had previously been regarded as poor offensive options, so Fairy's weaknesses to them gave them a new niche.
* There are several moves that block the user from taking damage that turn, most commonly Protect. Attempting to use Protect multiple turns in a row sharply slices its success rate to prevent indefinite stalling. Furthermore, similar guarding moves like Detect, Endure and Spiky Shield all work on the same mechanic, so you can't just alternate between two such moves to avoid the success rate degradation.
* The games had constant problems with the Pokémon Wobbuffet. Designed after a punching bag, Wobbuffet cannot attack directly but must return an opponent's damage with interest. However, in its debut generation, nothing stopped the opponent from just switching out over and over while Wobbuffet burned all of its PP. When Generation III introduced abilities, Wobbuffet and its new baby form Wynaut got Shadow Tag, which prevents the opponent from switching out, to compensate. Unfortunately, in competitive matches, you could easily end up in a draw if two Wobbuffets with Leftovers ended up facing off, as neither could switch out or do enough damage to knock the other out. Generation IV quickly adjusted Shadow Tag so that it also granted immunity against its own effect, and the self-damage calculation for Struggle got altered to make it depend on the user's maximum health rather than the damage dealt to the target.
* In the fifth generation of games, there was a glitch involving the new move Sky Drop. The move makes one Pokémon take another into the air (and then drop it for damage), and when a Pokémon is in the air, it cannot move or be hit (except by a few moves, like Thunder). There was previously a move called Gravity which made Flying-types or levitating Pokémon come to the ground (this meaning they can be hit by Ground-type moves). In a double battle, if one of your Pokémon uses Sky Drop and the other then uses Gravity, both Pokémon will come to the ground... [[GameBreakingBug except while your Pokémon can move, theirs is treated as being in the air and cannot move, at all, until they are fainted by a move like, say, Thunder.]] The Obvious Rule Patch? Nintendo banned Sky Drop in Random online battles.
* In the fourth and fifth generation games, there were problems with [[RageQuit players disconnecting to preserve their win-loss record.]] In ''VideoGame/PokemonXAndY'', however, disconnecting on players will count as a loss to the player who shut their game off.
* Pokémon with Oblivious as an Ability are immune to Infatuation, a status almost never used in any serious competition. In ''VideoGame/PokemonXAndY'', however, Pokémon with Oblivious were also now immune to the move Taunt, and specifically that move, essentially repurposing an Ability for an entirely different purpose (but one still marginally related to [[CaptainOblivious obliviousness]]). ''VideoGame/PokemonSwordAndShield'' would later add immunity to Intimidate, an Ability that lowers physical Attack.
* A meta example: when {{Website/Smogon}} decided that Mega Rayquaza was too much of a GameBreaker even for the [[CharacterTiers Uber tier]], they created the "Anything Goes" tier so they had somewhere to ban it to. The rules for Anything Goes are just what they sound like -- no bans, no restrictions... except that even in Anything Goes, the "Endless Battle" clause forbids movesets designed to [[{{Troll}} extend the battle indefinitely just to piss the other player off]].
** The Endless Battle Clause itself had to be modified several times to account for [[{{Troll}} certain creative types]] finding ways around the convoluted ban, which at its core involved a Leppa Berry [[note]][[ManaPotion Restores 10 PP to any move that runs out of PP]][[/note]], the move Recycle [[note]]Recovers a used item, such as a Leppa Berry; in this case allowing infinite PP restoration[[/note]], and some method of keeping the opponent from suiciding from Struggle recoil, of which there are shockingly many methods.
** ''VideoGame/PokemonBlackAndWhite'' gave Politoed the ability to make permanent rain, which gives numerous bonuses to certain Pokémon (including increasing the power of water type moves and activating certain abilities). One of these abilities, Swift Swim, doubled the Pokémon's speed under rain. At the beginning of Black and White, Politoed plus Swift Swim sweepers ran wild over the game. Smogon came up with a complex ban. Politoed could not be on a team with a Swift Swim Pokémon.
** Smogon tier lists are usually determined by usage. The more a Pokémon is used, the higher the tier it is in, the logic being that players will use the better more often. However, there were Pokémon that were not used enough to be useful in a higher tier but came to utterly dominate some lower tier. For example, in Black and White, no one would use Kyurem in Overused, but it completely destroyed most Pokémon in Underused. Smogon created "borderline" (now called ban lists) for Pokémon that are too good to be used in one tier but not used enough to be placed into a higher tier.
** Originally, tier lists were determined only by usage. After a user named "ihabt" decided to use several Neverused Pokémon in Rarelyused with terrible movesets and setups frequently with the intent of moving them up to Rarelyused, Smogon changed things to that such a Pokémon can't just be used in a specific tier, it needs to be viable and capable of winning enough battles in that tier as well.
* On the SelfImposedChallenge side, some Nuzlocke runs of later generations will have additional rules to account for new mechanics not present in Generation 3, where the ''Webcomic/NuzlockeComics'' originated. For example, ''VideoGame/PokemonOmegaRubyAndAlphaSapphire'' introduced the [=DexNav=] and sneaking through grass, which would make the Nuzlocke rule of "You can only catch the first encounter on a route" a complete joke since getting a really good first encounter would be incredibly easy. Possible rule patches for this would be to either forbid using the [=DexNav=] entirely, forbid sneaking through grass to get to a detected Pokémon until you're right next to it, or consider the first detected Pokémon the first encounter (so if it's not ideal, too bad, and if you give it up, you can't try again).
* In its original appearance in ''VideoGame/PokemonRubyAndSapphire'', the Pickup ability was a classic DiscOneNuke. Since it's available on a ComMon that pretty much everyone catches immediately and it has the chance of acquiring excellent items that players typically have to grind for (including, most famously, [[RareCandy Rare Candies]]), it takes practically no effort to grind out an item trove that allows a player to roll over most of the game. In later games, it was tweaked so that the list of possible finds was dependent on the level of the Pickup user - it still had the potential for some of the best items in the game, but a Pickup user had to be higher level to get them, and the lower levels still would garner some useful items; just not unbalancingly useful ones.
* The introduction of non-legendary Pokémon with the abilities Drought, Drizzle, Snow Warning, and Sandstream (which would set up sunny, rainy, hail (now replaced by snowy), or sandstorm weather respectively) in Generation IV led to the so-called Weather Wars, in which the metagame (both in Smogon and Nintendo-sanctioned tournaments) stagnated around setting up the player's preferred type of weather (generally by simply sending out something with the appropriate ability) and using a team built around getting buffs from said weather (most famously, rain teams built around the aforementioned Politoed). Generation VI finally brought balance by making weather-inducing abilities function the same as the moves that induced weather and giving them a 5-turn limit (with a held item extending it up to eight turns).
* In ''VideoGame/PokemonDiamondAndPearl'', you received the National Pokédex upon seeing every Pokémon in the Sinnoh Pokédex. The idea was that you would only achieve this after beating the Elite Four, in which you can get Palkia (Diamond) or Dialga (Pearl) recorded into the Pokédex; but it was possible to achieve filling out the Sinnoh Pokédex through trading and thus get the National Pokédex before beating the game. Come ''[[UpdatedRerelease Pokémon Platinum]]'' and in addition to seeing every Pokémon in the Sinnoh Pokédex, you also have to have beaten the Elite Four in order to get the National Pokédex.
* Mega Rayquaza is different from other [[SuperMode Mega Evolutions]] in that Rayquaza doesn't need to hold a specific Mega Stone to transform, and can therefore hold any item it wants. When ''VideoGame/PokemonSunAndMoon'' introduced Z-Moves (powerful attacks that can only be used once), a Rayquaza holding a Z-Crystal cannot Mega Evolve, preventing it from using both gimmicks at the same time.
** The games have [[DevelopersForesight gone out of their way]] to ensure a Mega-Evolved Pokémon can't use a Z-Move under any circumstances. Example; if a Pokémon holding a Z-Crystal uses Transform or the Imposter ability to transform into a Mega Pokémon, if it tries to use a Z-Move it'll say that there's no compatible move even if it knows a move of a matching type.
* While a player can have both a Dusk Mane Necrozma and a Dawn Wings Necrozma in their party in ''VideoGame/PokemonUltraSunAndUltraMoon'', only one of them can transform into Ultra Necrozma per battle; transforming one will prevent the other from doing so, even if the transformed Necrozma faints.
* Moves that [[NoItemUseForYou take away a held item or otherwise supresses them]] (like Thief, Knock Off, and Magic Room) won't work on specific Pokémon holding items that they have unique interactions with (such as Arceus's Plates, Giratina's Griseous Orb, Genesect's Drives, and any Pokémon's specific Mega Stone), nor do they work on Z-Crystals. Stealing moves (and Fling) also won't work on those items if the user is a Pokémon that can use them (e.g. Arceus cannot steal an opponent's Plate or Fling its own Plate at them), and Z-Crystals are unaffected.
* ''[[VideoGame/PokemonLetsGoPikachuAndEevee Let's Go Pikachu and Eevee]]'' added the ability to access the Pokémon Storage System at any time, instead of needing to return to a Pokémon Center. Accordingly, it removed the [[AntiFrustrationFeatures Anti-Frustration Feature]] added in Generation II that instantly fully heals Pokémon deposited into a Box.
* Mimikyu's Disguise Ability meant that it could shrug off one attack per battle until it faints, regardless of power. This means that giving it the Focus Sash will allow it to survive at least two hits that would have knocked it out in one hit. ''[[VideoGame/PokemonSwordAndShield Sword and Shield]]'' made it so that it loses 1/8 of its max HP after it shrugs off the hit so that the attack wasn't completely in vain.
** Speaking of the Focus Sash, prior to Gen VI, a Pokémon holding a Focus Sash would be able to shrug off all attacks from multi-hit moves like Rock Blast or Pin Missile. Afterwards, it only works on the first attack of such moves.
* Abilities that [[GeoEffects automatically generate terrain when the Pokémon is brought in]]--Grassy Surge, Misty Surge, Psychic Surge, and Electric Surge--were introduced in ''VideoGame/PokemonSunAndMoon''. Among other effects, most of them they granted a 50% boost in damage to their corresponding types, like Grass with Grassy Terrain. At the time, only the Alolan Island Guardians could have these Abilities, and that boost caused them to have such immense damaging power that they could not only plow through in-game challenges, but they could be found on most people's competitive teams in all battling modes. For ''VideoGame/PokemonSwordAndShield'', the damage boost with active terrain was reduced to 30%. Its "Isle of Armor" DLC campaign also added in the move Steel Roller, a very high-damage Steel-type attack that removes any terrain in the battle. All of the Island Guardians are part-Fairy, which is weak to Steel-type attacks.
* Shedinja, a Bug/Ghost type Pokémon, has its HP permanently set to 1 to counter its ability, Wonder Guard. This blocks it from taking any direct damage that does not hit it super effectively, though it is still vulnerable to damage over time effects, damaging weather, abilities and items. Since it has ''five'' weaknesses, it's also pretty easy to counter on that front, leaving it basically unusable apart from a few gimmicks like hard countering Kyogre. However, wouldn't it be nice if you could drop Wonder Guard onto, say, Sableye? Which until Generation VI[[note]]Introduced the Fairy type, which is strong against Dark, while Ghost cannot resist it[[/note]] had no weaknesses at all? Nope! Banned! Can't be done, as moves like [[PowerCopying Role Play and Skill Swap]] are programmed to fail if used on this ability. The only way to get Wonder Guard onto another Pokémon is via Trace, or having Shedinja use Mimic to copy the move Entrainment, the former being only possible for your opponent and the second only being usable in Double Battles and [[AwesomeButImpractical requiring significant setup that can easily be stopped.]]

* The UsefulNotes/VirtualConsole release of ''VideoGame/PokemonRedAndBlue'' does not allow Save States (a standard feature for other Virtual Console games released on the UsefulNotes/Nintendo3DS) to prevent players from cloning Pokémon, and prevents players from transferring [[OlympusMons Mew]] obtained through a glitch. In addition, all Pokémon transferred have their Hidden Abilities, otherwise people could use an Ability Capsule on Machamp to give it No Guard to ensure [[OneHitKill Fissure]] (which the TM for only existed in Gen I) would always land.
* ''Yellow'' changes the interaction with the Old Man in Viridian City who teaches you how to catch Pokémon from ''Red'' and ''Blue''. Thus, he can no longer be used to trigger the [=MissingNo=] glitch.

* [[invoked]] Yellow version, which is premised on being a RecursiveAdaptation of the anime and thus gives you Pikachu and only Pikachu as your starter, rewired the appearance distribution and movelists of some early Pokémon to mitigate the natural DifficultySpike given to Brock, whose Pokémon are all part Ground-type. Mankey becomes available west of Viridian City, both Nidoran learn Double Kick at level nine, and Butterfree learns Confusion at level ten, immediately upon evolving.

* Generation I was rather notorious for a number of poor balance decisions that had to be fixed in Generation II.
** Psychic-types in Generation I were very broken. Nothing resisted Psychic moves except Psychic itself, and its intended weaknesses, Bug and Ghost, suffered from underpowered moves and weak rosters, as well as a programming error that made Ghost completely ineffective on Psychics. When Generation II rolled around, the developers added two new types to act as counters: Dark did super-effective damage against Psychic while being [[NoSell completely immune]] to Psychic moves in return, while Steel simply resisted Psychic moves.[[note]] These types were not created ''solely'' to counter Psychic, but that was arguably their biggest impact.[[/note]] Meanwhile, Ghost moves became properly effective against Psychic as intended, and both Ghost and Bug got stronger moves and more capable Pokémon.
** Unlike physical moves, special moves used the same stat for both attacking and defending. This meant that while an individual Pokémon could be good at using physical moves but bad at defending against them or vice versa, being good at using special moves automatically made a Pokémon good at defending against them. Add in the move Amnesia, which boosted the Special stat by two stages, and a Special-oriented Pokémon could quickly become a nightmare to take down. To make matters worse, at this point in the series, a move's type was what determined whether it was physical or special, and Psychic was one of the special types; see above for why this was such a bad thing. Generation II wisely split the Special stat into Special Attack and Special Defense, putting physical and special moves on more even footing, and later generations would determine which moves used which offensive stat (ie Physical Attack or Special Attack) on a move-by-move basis, and not base it on the type of the attack. For example, the elemental punches were all considered physical attacks in later generations.
** Critical hits and instant-KO moves were both dependent on the user's Speed stat, to the point where faster Pokémon were almost guaranteed to crit. Furthermore, multi-hit moves would always crit on every hit or none per use. Generation II made the critical hit rate dependent on the move used instead and had multi-hit moves calculate crit chance independently for each hit, while instant-KO moves changed to depend on the level difference between the user and the target. That said, it wasn't a total loss for critical hits, since Gen II also fixed several bugs regarding critical hit chance and allowed critical hits to benefit from stat boosts during damage calculations.
** Hyper Beam had a number of ways to bypass the cooldown turn after use, such as if it misses, the target faints, or it broke a Substitute. Come Generation II, all of these loopholes have been closed to give the move more of a downside.
** Certain ongoing-damage moves such as Wrap would trap the target, rendering them completely unable to act for the duration. As of Generation II, the target still gets to attack; such moves now deal damage every turn without restricting a target's speed or ability to act.
** Struggle, the unique move reserved for when a Pokémon runs out of PP, behaved as a Normal move, which made it completely unable to affect Ghost-types. Later games would have it behave as a "typeless" move instead.

* Dark Void is a very powerful move in Double Battles (putting both opposing Pokémon to sleep), normally mitigated by it being exclusive to [[OlympusMons Darkrai]], a Pokémon normally banned in competitions. However, Smeargle can learn any move in the game through Sketch, and as a result Dark Void Smeargle ran rampant through the Video Game Championships scene for years, annoying players to no end due to how difficult it was to counter. ''VideoGame/PokemonSunAndMoon'' not only [[{{Nerf}} Nerfed Dark Void's accuracy to 50%]], but made it ''automatically fail if used by any Pokémon other than Darkrai''.