The Binding of Isaac has a load of content, thanks to being worked on for nearly a decade. Unfortunately, said content is bound to come up with infuriating design choices and mechanics that feel plain unfair at times, particularly after updates that introduce nerfs and buffs. Fortunately, many of these mechanics have been fixed or completely removed as the game has received updates and expansions.
Original game
- The Sacrifice rooms were notoriously worthless in the Flash version and Rebirth. They provide a small chance to spawn a chest upon taking damage from a spike tile in the middle of the room. The odds are so stacked against you that you usually have to drop down to minimal health or die for the chest to spawn, with no guarantee that it'd contain anything worth that health investment. Their only other purpose was to reveal how to unlock the Lost, so they were mostly avoided. Afterbirth overhauled the Sacrifice rooms, the tier of reward changing based on how many times you have hurt yourself, though they're still too luck-based to be relied upon; on the upside, they provide the quickest way to finish the Mega Satan and The Lamb path and are now used to directly unlock the Lost.
- In the original game, the Polaroid trinket, which automatically drops from Mom once unlocked, is needed to enter the Chest. Unless you have Mom's Purse to double your trinket capacity, this means sacrificing a potentially useful trinket for four levels in order to reach that path. If you were unlucky enough to grab the Tick (which can't be removed), the Chest is inaccessible. Rebirth fixed this by turning it into a passive collectible, though this comes at the cost of Mom dropping a potentially useful item. The Eternal Edition of the original made Mom's Purse a guaranteed drop from Mom, making it so that while you lose a regular boss item, you get to keep both trinkets and the Tick won't screw you over.
- Assembling a Meat Boy for the corresponding achievement was a simple task that became increasingly unlikely in later editions. A maxed-out Meat Boy requires four Cubes of Meat, which only drop from the Harbinger bosses, with one Harbinger being in the boss pool for each chapter. The introduction of the Headless Horseman (in the Flash game's Halloween update) and Conquest (in Wrath of the Lamb) complicated this, as either one can replace certain Harbingers but only drop their respective Pony item instead of a Cube of Meat; it's very easy for them to show up during a run and ruin your chances of getting the last Cube of Meat. Rebirth made it an even bigger Luck-Based Mission; the introduction of the Ball of Bandages means that finding a Harbinger doesn't guarantee you'll get the item you need, and the Book of Revelations (which overrides the floor's boss with a Harbinger if possible) is in less item pools and won't affect double-size boss rooms. Combined with the increasing size of boss pools, by the later expansions of Rebirth it's much easier to use outside sources (Monster Manual, Box of Friends, or Tainted Cain for duplication, or Potato Peeler in exchange for heart containers) to obtain Meat Boy or Bandage Girl than it is to get one the standard way.
Rebirth
- Angel Rooms were guaranteed to contain a free item in the Flash version, but in Rebirth they more often than not contain pickups, which generally aren't nearly as helpful. Additionally, to get them to appear, you have to pass up a Deal with the Devil, which more often than not grants items whose power more than justify the health cost and are usually much better than the standard Angel Room fare. Players usually only deal with Angel Rooms in order to take on Mega Satan, which requires you to find two of them in the same run (or mess with a Sacrifice room), which doesn't always happen even with optimal circumstances and can force you to skip items like Brimstone. This was addressed in the second booster pack update for Afterbirth+, which makes item spawns more frequent and sometimes allows you to choose between multiple items, increasing the chances for players to get something useful out of the Angel Rooms. Repentance gave them even more buffs, both indirect (many devil items were nerfed to become much less game-breaking) and direct (an angel room is guaranteed to spawn the next time a special room appears if you skip the first Devil Deal to spawn; the Angel Room's item pool received many rare yet extremely powerful items like Revelation and Sacred Orb), to the point that there is a very good argument for Angel Rooms being better than Devil Rooms.
- Curses. Unlike similar mechanics that serve as a risk/reward type thing like Champion monsters that are harder but drop better items, things you can choose to opt out of like Curse Rooms (take damage for the chance of items), Planetariums (that require you to skip several Item Rooms for one higher-tier item), or a Deal with the Devil (trade vitality for a new power), curses are nothing more than a mechanic where the game arbitrarily decides to greatly hinder, annoy, or generally screw over the player while offering nothing in return. It's exacerbated by how the odds of a curse steadily increases as you complete aspects of the game — defeating Isaac even once jumps it to a brutal 20% chance of a curse per floor, meaning you're more likely to get a curse than you are to get a Devil Room and making the game borderline unplayable. While losing a run due to a bad item combo or because you chose to gamble and lost feels like your fault, losing a run due to a curse just feels unfair, and it's very telling people were so fed up with this mechanic that there exist several mods to remove them outright.note To wit:
- Curse of the Blind has the effect of making you unable to see the pedestal items on that floor, replacing them with a question mark icon. This can screw a run in so many ways, given the risk of spending health/money on something worthless or picking up a very disadvantageous item by accident. The whole floor becomes a roulette wheel you can either try for potential help or ignore for a lost floor of items. The worst of it is when you manage to land the curse on The Chest, where the starting room gives you four free items.
- Curse of the Maze causes you to, at random times, warp across the map to a random room when passing through a door. This can transport one from a cleared room to another cleared room, and sometimes even warp you to the room you already came from, wasting time instead of increasing the risk of traversing the floor. The curse will also shuffle around some of the contents of the floor, which can send something in one room clear across the map. At best, it's considered an annoyance that barely raises the difficulty, and at worst, you could be pushed just over the 20/30 minute mark and get locked out of the Boss Rush/Hush battle due to the time spent fighting against a particularly large Curse of the Maze floor and hoping that the RNG will just let you go where you want to. Repentance changed the curse so that it can only send you to undiscovered rooms, reducing its annoyance.
- Curse of the Labyrinth merges both floors of a chapter into one single massive level with two bosses and two item rooms. Unlike other curses, which just have a good chance of ruining an otherwise good run but can be weathered no worse for wear, this one is a guaranteed turd to the face, as it means you are guaranteed one less Devil/Angel Room, one less shop, and two less secret rooms. This can massively hold you back, especially if you've rolled particularly unlucky on resources so far.
- Curse of the Unknown makes it so that you cannot see your remaining health. This is no problem if you're playing The Lost/Tainted Lost, but as any other character, this becomes worrisome. It may cause you to constantly feel uncomfortable, not knowing if the next hit will be your demise. It also makes using Blood Donation Machines, Devil Beggars, Confessionals, or other "damage yourself for rewards" mechanics outrageously risky, since you won't know whether or not you actually have health to spare.
- Curse of Darkness makes the game so dark it's almost impossible to see, which means you'll be taking a lot of damage you'd normally not be taking since you'll constantly be running into small dark enemies like spiders, or getting caught on terrain trying to dodge an attack. On an already dark map like the Necropolis or Sheol, you might as well reset.
- Several of the challenges have the Blindfolded mechanic, which completely disables Isaac's ability to fire tears, including Mom's Knife. Not only does this make killing enemies a lot more difficult, but all of the associated challenges also saddle you with terrible loadouts, relying on orbitals, familiars, and bombs to take out enemies, leading to either poor damage output or constant risks.
- The "special items" pool was a mechanic in the Flash version of the game to lower the chances of getting tons of overpowered items, but only became disliked in Rebirth. While less items are counted as special, merely seeing any of them is enough to increase the chance that a later special item will be invisibly re-rolled into something else, regardless of whether you take it or not. This even applies during Curse of the Blind; if you go into a devil room with the curse active, and one of the hidden deals you don't take is Brimstone, you'll have your special item chances cut and never know why. Being locked out of game-breaking items is generally considered an unfair disadvantage, especially since the pool originally contained unfitting and controversial items like Soy Milk, Lil Brimstone, and Stop Watch. Later expansions stopped considering these to be special items, and Repentance cut the mechanic in favor of item quality and weight.
- Greed and Super Greed. When you encounter them in a secret room, it's great, since they go down easily and give a decent dose of coins or the Steam Sale item. But they're far more annoying to see instead of a shop, since you're very likely to encounter them when you already have enough coins and are wanting to buy items — in other words, you miss out on one of your limited shop visits in exchange for either a mediocre handful of coins or an item that doesn't serve any purpose without access to a shop. If that's not bad enough, it's possible to run into both of them in the same run, losing two separate opportunities to buy stuff. They're even worse during challenge runs, since these runs lack free item rooms, which means Greed and Super Greed in effect steal one of your very rare opportunities to get a new item. They hurt Tainted Keeper especially, because the character is heavily reliant on shops to get good items early in the run.
Afterbirth
- Greed Mode ends with a special version of the donation machine, which unlocks new items and starting bonuses for characters as it is filled up. However, it can jam just like the donation machine on a normal run, meaning that all the coins you gather across a Greed Mode attempt can be rendered worthless if it jams after just a couple of pennies. The machine's jam percentage varies per character to encourage switching around, but even with optimal luck, it takes a ton of runs of a 20-minute arena mode to max out the machine. The same patch that added Keeper made it take many more coins to jam the machine, allowing the process to go by quicker.
- Afterbirth introduces damage scaling for its two new superbosses. To encourage more defensive builds, in addition to having high health pools and focusing a lot more on learning their different attacks, the bosses also have a mechanic where their defense increases based on how much damage you're outputting. As a result, a run that would normally stomp every other boss is forced to have a long endurance match against them, which can get tiring across several playthroughs. In very rare cases, having too high of a damage output can break the damage resistance and make the boss nearly impossible to kill. But on the bright side, it does keep bosses like Hush and Ultra Greed from becoming Anti-Climax Bosses.
- Half-size rooms are not ideal to see due to the number of enemy encounters that aren't designed around cramped spaces. For example, Krampus and the Forsaken have rotating Brimstone attacks, which become unavoidable if they're hugging the wall, and in a half-size room, that's virtually always the case. A patch reduced the odds of half-sized rooms appearing, with Repentance removing half-sized boss rooms entirely.
- Pills became a scrappy mechanic around the time of Afterbirth, with many players refusing to use them at all. Many new pill effects were introduced, most of which were considered neutral (meaning PHD, Virgo, and Luck Foot don't override them) despite having poor or negative effects. Some were also the reward for completing challenges, which diluted the effect pool even more. The worst by far is the Retro Vision pill, which periodically pixellates the screen for a short time, an annoying effect that can cause eye strain and lag. Repentance replaced the filtering effect with a sprite-downscaling effect that was less intrusive, and generally improved the quality of pills.
- The Schwag Bonus is disliked in terms of the competitive nature of daily runs. It is a point bonus based on the pickups collected, and has an extremely high cap corresponding to far more collectibles than any standard run would ever need. This can easily be exploited with game-breaking items that result in spawning a near-endless number of pickups. Because of that, daily runs feel much less based on skill than they do on searching for the Shop and things related to making money, and finding ways to break the system with Restock, Blank Card/Jera, and the like. Thanks to Mama Mega being used to open the Boss Rush/Hush at any time rather than before the 20/30 minute mark, allowing for the player to take their time for the Rush Bonus, and the Clicker removing a passive item, allowing for a smaller Item Penalty, the results in the highest score being given to those patient enough to work on the given game-breaking method of the run.
- Defeating the Boss Rush as Keeper unlocks Sticky Nickels, which are unable to be picked up unless they are hit with an explosion. While they were intended to have a chance of replacing pennies, effectively making nickels more common with a trade-off, they instead have a chance of replacing regular nickels, making the unlock strictly a downgrade.
Afterbirth+
- Delirium's shapeshifting and Teleport Spam can create unavoidable damage due the fight being unpolished. If Delirium shifts from Mom's foot to anything else, if it hasn't stomped, you take instant damage, and it can shift into a Dual Boss right on top of you. This renders winning with the Lost and especially Tainted Lost a Luck-Based Mission for the most part.
- Accessing The Void in the first place is almost entirely down to luck. After being unlocked, each of the game's various end-game bosses has a chance to spawn a portal to the final floor, highest being a 50% chance to appear after defeating Mega Satan. There is a way to guarantee a portal spawn, but this requires you to defeat Hush in your run. This will always open up a separate room that has a portal in it. Problem is, Delirium is one of the most difficult bosses in the game, so it is advisable to do as much preparation and get as many items as possible. Doing it this way not only means you have to rush through the game, but also skip out on The Chest/Dark Room and miss a lot of potentially useful items.
Repentance
- In order to enter the alternate floors, you need to spend one key to reach Downpour, two bombs to reach the Mines, and two hearts to reach the Mausoleum. This requires you to sacrifice pickups early in the game that could otherwise be spent to give you an advantage, and running out forces you back onto the main path, locking you out of getting the two Knife Pieces you need to reach the Corpse. The heart requirement for the Mausoleum is especially annoying, since it takes temporary hearts before red hearts and cuts into the health of characters that can't gain permanent heart containers. Additionally, trapdoors always lead to the next "classic" floor, which means that doing anything that locks you into I AM ERROR can deviate you possibly permanently from the alternate path and its final boss.
- Getting the second Knife Piece. While it is an undeniably awesome and adrenaline-inducing moment the first time you experience it, having to do the entire chase sequence with very minor variation each time you want to go to the Corpse can get old, especially considering how easy it tends to be once the initial shock wears off, and since in Antibirth the Knife puzzles only required you to solve them once, and they would be permanently unlocked on every subsequent run.
- It's only slightly better if playing as the Lost, Tainted Lost/The Baleful, or Tainted Forgotten/The Fettered, as the Mausoleum door opens for free without hurting them. Given their status as really difficult characters to play, this is the one guaranteed blessing they'll have on the alt path.
- In order to get to Mother, you need to go to Downpour to get Knife Piece 1 and Mines to get Knife Piece 2, then stab the fleshy door to beat Mom's Heart. The alternate floors are very hard compared to the normal floors, making Mother the hardest boss to access in the game. Although Cracked Orb and Sharp Key can make the unlocks easier, skipping Knife Piece 1 and 2, it doesn't make it much harder compared to accessing The Beast, Mega Satan, and Delirium. Oh, and the worst part is if you want Infinity% you have to do it 34 times.
- Unlocking Planetariums in Repentance is even harder than it was in Antibirth. In either game, you have to find three astrology-related items on a single run by chance, but this is compounded in Repentance due to the item pools being three times as large and there being less items that count towards it. A patch added more items to this pool, but it's still relatively small.
- The primary gimmick of Tainted Jacob is having to run from Dark Esau. After a short time on every floor, he'll spawn in and start chasing after you, damaging enemies he touches. If he makes contact with Tainted Jacob, he "dies" and turns into The Lost for the rest of the floor, meaning you gain flight and spectral tears, but the next hit you take will kill you. Kind of annoying to work with, but learnable, and easy to use to your advantage — you even start with an item that can freeze him in place for a few seconds. The issue is that you also turn into The Lost if Dark Esau dies (yeah, he's not invincible). And unfortunately for you, Dark Esau is an idiot. He can, and will, blindly fly into damaging hazards, troll bomb explosions, and enemy Brimstone lasers that shave massive chunks off his HP, which can result in you turning into a One-Hit-Point Wonder due to something out of your control. What's more, auto-firing familiars like Demon Baby or Boiled Baby will shoot him if he's nearby, whittling down his HP even more.
- In the v1.7.5 update, Tainted Jacob was made even worse. For starters, Dark Esau is now invulnerable to all damage. While this does outright remove the risk of him accidentally dying to a factor outside of your control, it becomes a problem if you wish to slay him manually, like in the previous patch, because you can't. And it only gets worse from here. The v1.7.5 update adds the rest of the missing Birthright effects for each character. What does Tainted Jacob get? Upon picking up Birthright, Dark Esau DUPLICATES and splits himself into two. Now you have two demons following you that will slay you in one hit. It really says something when T. Jacob's description of Birthright reads, "It's not yours". RUN AWAY!!!
- Tainted Forgotten's gimmick is also liable to make you tear your hair out, though to a lesser extent. Rather than switching between the two, the Forgotten is invincible but immobile, requiring the Soul (who can't attack whatsoever and has to rely on the Forgotten) to pick him up and throw him at enemies. While this can result in some pretty strong damage, this comes at the downside that any items involving character placement (like familiars) or placing bombs are all centered on the Forgotten's location... instead of, you know, the Soul, the character you're actually controlling for the most part. Similarly, while you can throw the Forgotten through doors to shorten trips through the level and get into Curse Rooms without taking any damage, this benefit ends up becoming risky regarding bosses that spawn in the middle of the room, like Mom's Heart/It Lives!. For that boss in particular, the entrances to Sheol and the Cathedral spawn in the middle, and if the Forgotten happens to be sitting on either when they appear, you have only a microsecond to react before it registers the Forgotten being present and forcing you to enter the next level (which can ruin your plans if you want to do Hush, or try to go for the Chest with the Polaroid but get forced into Sheol instead). This can be fixed if you quickly dive in and throw the Forgotten anywhere else, but the fact that you have to do this after a boss kill reeks of Fake Difficulty.
- TMTRAINER's effect isn't well liked due to being wildly unpredictable; it replaces almost all pedestal items with "glitched" items that have random effects. While you may potentially get a Game-Breaker item out of it, you're equally as likely to get an item that will completely ruin your run.
- Prior to the v1.7.5 update, this effect had a bug that caused it to affect plot-important items like the Polaroid and the Negative, limiting your run options severely.
- If that wasn't enough, the "glitched" generation isn't limited to this, as unlocking the Corrupted Data achievement (unlocked by defeating Delirium as Tainted Eden) can potentially turn a secret room item into a "glitched" item, with no idea if its effects will be helpful until it's picked up. Don't forget, this is permanent on your save file!
- Haunted Chests are considered a Power Up Let Down. They are pale-tinted chests that have a Potly carry them and throw them at Isaac, dealing damage if he touches the chest even before the Potly appears. It comes off as the reverse of a reward. And it doesn't help that you unlock it by beating Mega Satan as Tainted Lost. It's another case of doing something very hard to make the game worse.
- Tainted Keeper's gimmick of needing to pay for every item but in exchange all enemies drop coins that rapidly despawn isn't normally problematic, and is even quite engaging and adds a level of risk-reward gameplay. In Co-Op however, every item still needs to be paid for, including the additional boss items spawned for each additional player, and to add insult to injury only enemies killed by Tainted Keeper drop coins. Good luck paying for them all.
