Obvious Rule Patch / Dungeons & Dragons 5th Edition

• The Haste spell gives the target an extra Action during their turn. Fifth Edition patched it so that the target can only do a few specific things with that Action: attack, dash, disengage, hide, or use an object. If you attack with the Haste Action, you can't attack more than once. Also, the target can't use the Haste Action to cast any spell, even the most basic cantrip. The reason is that two players with Haste could otherwise give each other an infinite number of turns: take an action, cast Haste on the other person, wait for them to do the same, then repeat until everything is dead. And just to make absolutely sure that the spell can't be abused, Haste also causes its target to lose their next turn after the spell ends.
• The Time Stop spell freezes time for everyone but the caster, giving you anywhere from two to five free turns while everything else is frozen in place. The spell was patched to end instantly if you use one of those turns to affect any creature other than yourself in any way, rather than just restricting attacks, and also ends when you leave its 1000 feet range.
• Buffs and area-of-effect spells in general used to be stacked on each other so often that dice rolls became patently ridiculous to calculate. The Advantage mechanic simplifies buffs significantly in this regard. If you have advantage, roll a d20 twice and take the highest number. If you have disadvantage, roll a d20 twice and take the lowest number. There are still other buffs that can activate, but it meant that combat calculations were a lot quicker.
• The Concentration mechanic was used to reduce the number of gigantic area-of-effect spells that covered the battlefield at one time, both for players and enemies. If a spell is labeled that it needs Concentration, casting another Concentration spell instantly ends the first Concentration spell since you can’t have more than one Concentration spell going simultaneously. In addition, if you take damage, you have to make a Constitution saving throw to maintain concentration, with the spell instantly ending if you fail. This makes several late-game spells much less intense, since there's at least a way to deal with them and keep the tension high.
• The Wish spell was changed so that there's several restrictions to it. Wishing for anything other than the effect of an 8th-level spell or lower imposes severe penalties: massive necrotic damage that can't be blocked, several days worth of being unable to do anything but lay in bed, temporary reduction of your Strength score down to 3 (the lowest it can be) for 2d4 days, and a one-in-three chance of becoming permanently unable to cast Wish ever again. This is because players made truly insane wishes with the spell — even assuming the DM wasn't being a Jackass Genie about it, Wish is called "the mightiest magic a mortal can wield" for a reason, since you could theoretically Wish for anything to happen. It's still a huge Game-Breaker if you can ever cast Wish, but it's not quite as much of a Game-Breaker as it used to be in other editions.
• Bardic Inspiration allows a player to roll a d6, and add the number to an attack roll or saving throw. However, all but a few of the Bard schools say that a Bard can't use Bardic Inspiration on themselves. This was done to avoid a Bard always self-targeting with their Inspiration over and over to ensure they pass on whatever they are rolling for, which would become a major problem as the Bardic Inspiration dice get better as they level.^note This also keeps the Bard more thematically appropriate by having them inspire others, as well as avoiding the odd logic of someone somehow persuading themselves into doing a better job.
• The Druid's Wild Shape allows them to turn into any creature of a certain Challenge Rating or below. What that Challenge Rating depends on the Druid's level, with some subclasses giving a wider range to pull from. However, the rules for Wild Shape state that a Druid can only turn into creatures they've seen before. This was done to prevent players from turning into rare creatures that their character would realistically not know about since rare creatures usually have unique abilities, making them appealing from a meta angle to use over something more common. So you won't see a Druid turn into a Giant Squid if they've never seen the ocean in their entire life, or see Druids turn into creatures from other planes that they realistically should never have seen before.
• When the Barbarian's Wild Soul subclass was still in playtesting, if a Barbarian rolled a 1 on a d8 for their Wild Surge, every creature within thirty feet took 1d12 necrotic damage and the Barbarian received that damage dealt plus their Barbarian level as temporary HP. This meant that a Barbarian could gain an absurd amount of temporary health that made them effectively invincible.^note For context: if a Barbarian was in a party of five and faced five enemies, the Barbarian could gain as much as 111 temporary HP, while just at level 3. When released, that Wild Surge instead only affected targets that the Barbarian wanted it to hit, it could be blocked with a Constitution saving throw, and the amount of temporary HP received was reduced to a flat 1d12, greatly reducing the power of the ability.invoked
• The Guidance cantrip is a spell that adds a d4 to one target's next ability check. While not that strong, having a spell like that be so easy to cast would potentially break the flow of the game. For this reason, the spell has both Verbal and Somatic requirements, meaning that you'll be noticed when you cast it; try this mid-conversation with an NPC, and they'll know you're up to something. It's also commonly balanced by a DM by making Guidance something one must declare before a roll is made, so as to avoid someone failing a check only for a Druid/Cleric to cast Guidance and ensure a success.
• Magic Jar allows a Wizard's spirit to leave their body, with the spirit going into a container made for the spell. From there, they can possess any humanoid creature within one-hundred feet, replacing their stats with the target's (except for Intelligence, Wisdom, and Charisma). When brought into Fifth Edition, Magic Jar was given adjustments to balance it. A target made a Charisma saving throw against being possessed; if the target passes the saving throw, they can't be possessed again for a full day. If the host body dies, then the caster must pass a Charisma save to return to their container or else they also die. And if the caster's body is dead or outside of the hundred-foot range, the caster's spirit dies as well. Finally, spells like Death Ward can't save someone who fails the Charisma save or moves out of range. Combined with the fact the container costs money and is destroyed after use, this balances Magic Jar and avoids making it a Game-Breaker.invoked
• Sorcerers can use their Font of Magic ability to convert their spell slots into Sorcery Points, then back into temporary spell slots of different levels. This normally isn't an issue, as you have a limit to how many Sorcery Points you can have at one time, and your spell slots and Sorcery Points both reset at the end of a long rest. However, if a Sorcerer takes levels in Warlock, they now have additional spell slots which return on a short rest. By taking numerous short rests to get their Warlock spell slots back, converting them into Sorcery Points, then into temporary spell slots, the Sorcerer/Warlock (commonly called Sorlock) can theoretically accrue an infinite number of spell slots as long as they don't long rest to reset their spell slots — this build was called a "Coffeelock", as it didn't sleep. Originally, the only penalty to not taking a long rest was that you didn't get back hit points or (for all classes except Warlock) spell slots/most abilities. In response, Xanathar's then introduced a rule which made characters who didn't long rest for multiple days take increasing levels of Exhaustion. While technically optional, this rule was widely adopted by DMs in order to stop Coffeelocks.
• The Sentinel feat gives you the ability to attack a creature near you when it attacks another target, but only if that target doesn't also have the Sentinel feat. Realistically this makes no sense, but mechanically it's intended to prevent a creature from being surrounded by characters with Sentinel, so they get attacked no matter who they target.
• The Shield spell gives the user five extra points to their AC, and also specifically mentions blocking Magic Missile. As specific as this is, it's to make sure there is some way to block Magic Missile from always hitting since it is one of the very few offensive spells that just hits without the need for any rolls to do so, and without it, Shield would have no real value against enemy casters.
• The Sanctuary spell forces enemies that attack the intended target to have to make a Wisdom saving throw, or else they have to attack another target or waste the attack/spell they were using, but the effect vanishes if the warded person makes an attack, casts a spell that affects an enemy, or deals damage to another creature. The "deals damage to another creature" rule was later added to specifically address exploits of the spell where people would cast it on someone, and then use summoned creatures or beings to do the damage for them since technically the user wasn't doing damage. This led to Cleric's making Sanctuary and Spirit Guardians combos that were really powerful, so the last part was added to Sanctuary to address that.
• In addition to the Divine Smite they get at level 2, paladins can learn spells that function like Divine Smite, such as Searing Smite. To account for the fact that a Paladin is likely to want to use Divine Smite and one of the Smite spells, the Smite spells were made Bonus Actions so the Paladin can actually cast and attack, but were made Concentration spells to balance it better. So a Paladin using Thunderous Smite can attack, but if they miss, they don't waste the spell, and have another chance to use it, but also have to be ready to make Concentration Checks to maintain the spell, helping make the spell Smites helpful, without being broken.
  • Divine Smite in general became a tricky subject. Divine Smites use spell slots but are not spell attacks and so they can be used even where spells cannot (for example an Anti-Magic Field). For 5E, Divine Smites were patched to require a melee weapon attack, with lead rules designer Jeremy Crawford specifically saying that unarmed strikes weren't weapons, but this led to a conflict with the rules for monks and ki-point attacks. After Crawford took some heat for this, this "patch" was removed so paladins can now channel holy power through their righteous fists.
• Many spells tend to have specific wording as to who they can be casted on, such as saying a "willing target", "not-hostile", etc. The specific wording is to prevent abuses in spells that should realistically not be able to be done; a caster cannot cast Haste on an enemy, only to deactivate it right away so the enemy is stunned for a round.

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