These are the bosses of the The Binding of Isaac series that are hair-pullingly frustrating to fight and/or tedious, and not because they are infamously difficult. Other bosses are relatively easy in comparison.
- Go ahead, try to mention Greed to anyone who's a veteran of this game without setting their blood to a boil. It's not just the fact that he's hard to fight without being hit once (his attacks are completely random and have no telegraphing whatsoever), but his appearance results in you losing the shop or secret room of that level. This can be annoying at best (meaning you've lost a key or bomb to get in for nothing), or utterly fatal (you so needed that shop for health or equipment...). The exception is when not having enough money, as Greed drops a lot of coins. And then, when you DO need coins, the game spawns a shop instead.
- And just because the developers love to see us cry, they've given us a Super Greed, who has a much wider bullet-spray (though it also means he can't hit you from the front), more health, and he spawns Keepers, enemies that eat your coins with each shot.
- Of course, the fight against him can be exploited if you're good at dodging. If you have the D6, getting an item from Greed can net you an item from the Shop or the Secret Room item pool. Add in some batteries, and you have yourself a recipe to get the most convenient item for your run from any of both pools, all from one boss! If you have the D20, you can simply reroll the money to obtain various powerups! And lastly, if you have Money = Power, you can power up your damage by simply defeating him! That being said... goddamned Greed!
- Greed's infamy as a boss extends to Afterbirth by giving him a game mode of his own in Greed mode. In fact, a much harder version of him appears as the mode's final boss.
- Afterbirth+ introduces the Greedier mode, which spawns less coins, has more powerful mooks, and each wave has a chance where Greed or Super Greed will appear. And the boss of Greed mode? Hooo boy...
- Envy, another Deadly Sin. While he has the same chance of spawning as the Sins other than Greed/Super Greed, Envy takes the cake for not being difficult to fight, just VERY tedious, especially when encountered on the first or second floor. He's an Asteroids Monster that splits in two (three as Super Envy) each time he's killed. He never attacks, just bounces around the room diagonally. And to top it off, while the other Sins drop potentially useful pickups on death, Envy leaves behind a Troll Bomb. While not particularly tough, the fight takes forever if you have no damage upgrades, to the point where, if found early on the run, many players will just reboot a run right then and there rather than put up with him. No wonder he has a constant Troll Face on him.
- Sloth, another Deadly Sin, can also be this if your damage or fire rate aren't high enough. He shoots Ipecac bombs at you, which have a good radius and deal hefty damage. Additionally, he spawns Chargers, which will cause you to either focus your fire on them while dealing with Sloth's Ipecac shots, or keep firing at Sloth while avoiding a bite from the Chargers.
- The Super variants of the Seven Deadly Sins are this. Super Greed spawns Keepers and has a wider bullet spread attack. Super Lust is faster and leaves a damaging red blood trail. Super Sloth constantly spawns Spiders and shoots more Ipecac bombs. Super Pride spawns Mega Troll Bombs instead of regular ones and shoots projectiles that make it more difficult to avoid the diagonal tentacle/shock attack. Super Gluttony launches a spray of bullets in addition to the usual spread of bullets and fires Brimstone lasers in two directions. Super Wrath fires Mega Troll Bombs instead of normal ones. And Super Envy divides into many more versions of itself, making for a longer fight. Their attacks still deal one full heart of damage, so be prepared to face them with high health.
- Gemini can be this to less experienced players. They're one of the earliest bosses you can fight in any run and have above average healthnote , and it might seem like a fairly easy boss to hit because of the size of Contusion (the larger twin), but he can suddenly start running as fast, if not slightly faster, than you. Thankfully, he stops to catch his breath every once in a while, allowing you to hit him or his smaller twin brother Suture, who constantly shoots at you if you get near the twins. Once Contusion is down, Suture will take action and chase you; not only can he fly over obstacles, but he can cut corners and catch you out in the mess of obstacles that normally spawn in the room as well. The fight can take long enough as it is depending on your starting build, so patience is key.
- Their alternate variant, Steven, is slightly harder. Once the bigger Steven is damaged enough, the smaller Steven will take action early, forcing you to fend off the small twin as the bigger one chases you. They also have the added trait of shooting bullets for each twin that is killed.
- Rebirth adds Dingle and Dangle, living poop monsters which are Gurdy Jr.'s annoying cousins. In addition to possessing the same charge attack as Gurdy Jr., they will do it three times in a row (Dingle's red champion variant will do it four times instead, whereas the black champion variant only does it once, but faster). They also have a bullet attack and spawn mooks. On early floors when your speed is low, there's a good chance one of their charges may connect. Their health is also one of the highest of any first floor bossnote , so you'll stay a while fighting these things.
- The Green champion Duke of Flies when you don't have any bombs or piercing shots. He spawns Moters as he bounces around the room, which can be dangerous if shot, as they split into two additional Attack Flies upon death, making it hard to get a hit on The Duke himself.
- For that matter, any variation of the Duke of Flies can be this; he's one of the easiest bosses to beat since it has pitiful healthnote , but his battle will take quite some time, especially whenever he's the first or second boss to appear in a run, which makes trying to shoot through his fly mooks extremely annoying. In fact, when you later see him as a Degraded Boss in the Womb or Sheol, it often turns into a Curb-Stomp Battle in your favor.
- His posthumous version, The Husk, is just as annoying. He bounces around the room faster, can summon flies as well as spiders, and he fires bullets when he disperses his flies. As such, while it's definitely possible to beat this fight without damage, you might get hit once or twice if your damage isn't high and you're not careful enough. Thankfully, Husk has low healthnote for a boss of his floor.
- The Widow, a first-floor boss that jumps around like crazy, spits demonic spiders (the tiny kind), and spawns sacs that in turn spawn more spiders. Her saving grace is that her health is rather low for a boss of her sizenote , and she's huge, so hitting her is surprisingly very easy. Her posthumous version, The Wretched, is just as annoying, since she spawns even more spiders, big spiders that divide into two on death, and Trites, spiders that can hop around, although her health is also lownote . They were actually tougher before, to the point both were considered That One Boss, but both were thankfully toned down after release.
- Afterbirth brought in an influx of rather challenging boss encounters... and then there's Little Horn. Despite his demonic appearance, he has average healthnote and some of his attacks aren't incredibly dangerous; he summons pits for you to fall into, opens one to throw a Troll Bomb at you, and fires a giant homing projectile that can be destroyed. Then what's the problem with him? That he never holds still. He's a first floor boss, meaning that you're unlikely to have any good items to speed up the process, and much of the fight has you chasing him and dealing chip damage as he teleports around the room dropping Troll Bombs, though his penchant for doing so often leads to him blowing himself up in a similar manner to Pin in the original game. If your speed and/or damage are even slightly decent, it's unlikely Little Horn will even manage a hit on you, but even then, chasing him will feel like a chore and you'll pray that he kills himself by teleporting into a bomb of his own.
- The v1.7.8a update buffs Little Horn and makes it so that he only takes 25 damage from his own troll bombs instead of 100 damage. Furthermore, the orange champion version now only throws flaming troll bombs.
- It's even worse on the black champion variant, which basically multiplies every frustrating thing about the boss. He no longer throws troll bombs at all, instead opting to teleport around and spit out dark balls constantly. That means he can no longer hit himself with explosions, and you have to constantly divide your attention between the slippery boss and the enemies he summons. And he's even less of a threat, since the only way he can possibly hit you is if you back yourself into a corner. You better hope there's a fireplace in his boss room that you can corral him into, otherwise you're in for a long fight.
- Gurdy, a Damage-Sponge Boss found in The Cavesnote , can't move but takes up half the room. She can fire five bullets in a spread pattern and summon flies, as well as Boils, sacs that fire more bullets. Compared to the other bosses, she takes a really long time to beat. It's easy enough if you get her pattern down, though. You also better hope you've upgraded your damage or fire rate, because Boils regenerate like spider sacs do. A lot easier if you learn to exploit the space behind her where flies spawn, even easier if she spawns an explosive Boil, which tends to hurt her more than you.
- Peep, another Damage-Sponge Boss from The Cavesnote . At first, he has the simple pattern of creating damaging urine around itself, hopping and firing eight bullets around it, or jumping high like Monstro and firing twelve bullets around himself. Once you damage Peep enough, however, his eyes will detach one by one from his face and bounce around the room, forcing you to avoid the bouncing eyes and making him harder to hit. The eyes also have a clunky collision detection that matches that of Peep. And the champion variants are more annoying, with the Dark Green champion detaching its eyes as soon as the battle starts, and the Yellow champion being capable of movement while leaving more damaging urine. It's impressive how The Bloat, even while alive, is capable of making players suffer...
- The Dark One doesn't have as much HP as the other bosses abovenote , but it's still above average for the floor it's in. The Dark One's main problem consists of it suddenly deciding to dash twice across the screen, wrapping around the walls and aiming for your location; this attack not only makes the Dark One harder to hit, but it also draws on the fight for longer than it should. And don't even think of walking below the Dark One and standing there to damage it, as it can suddenly fire a Brimstone beam with little tell, similarly to its posthumous version, The Adversary.
- Mega Fatty, yet another Damage-Sponge Boss, has the absolute highest HP of any boss found in the second floornote , and can spawn Dips, fart to create toxic gas around him, or suck up everything in the room (including you) only to follow up with a waterfall of puke. However, these attacks are not what actually make him a pain; it's his infamous jumping attack. As he lands, Mega Fatty spawns a pool of toxic blood around him. The kicker? He has a variation with no tell, so if you don't have enough speed to avoid him as he lands, this will hit you. With such a high health pool and this attack, you'll need to be really patient and have fast fingers. And of course, he has two Champion variations: the Red one has less health but shoots six bullets in an asterisk when he lands, and shoots a junior version of Mom's Heart's Bullet Hell attack (though you can avoid this by standing close to him so the bullets fly over you); meanwhile, the Brown variant has more health, and while he never uses his "puke waterfall" attack, he creates rock waves in random directions when he lands from his jumping attack. Sound familiar? That's because this is That One Attack for his posthumous version, The Cage.
- Monstro II is a huge step up from his first form. He's a damage-spongier version of the original one note . Instead of his disorganized belch bullet wave attack, he fires Brimstone lasers and eight large blood bullets that fly across the boss arena when he lands, and spawns Suckers, flies that split into blood bullets when they die. Fortunately, he can only shoot his Brimstone lasers if you pass his sides, and you can even trick him into this. You'll need skill to dodge the rest of his attacks and the Suckers, though.
- For that matter, while both Monstro's and Monstro II's attacks are only moderately dangerous (compared to the rest of the bosses), they have very high health compared to them (for their respective levels), making both fights boring and thus, prone to mistakes. They can also render themselves immune to most attacks just by jumping (which they'll be doing constantly), making it hard to hit them with bombs or certain pickups.
- Brownie has the qualities of a That One Boss. It has decently high healthnote for the floor it is found on, the ability to spawn Corny Dips at an alarming rate, it can leave corny mines that explode and send bullets flying in eight directions, and jumps and runs around while leaving slippery poop puddles and shooting big bullets at your location. He also recovers health if you have the Butt Bombs item and use it against him, or if he steps on the Corny Dips he summons. There's one thing that makes the fight against him annoying at best though, and it is that his own corny mines can deal huge damage to him and poison him in the process (although he does leave damaging green, toxic puddles if it happens). Unless you have low damage and/or fire rate, Brownie is easier in practice than it is on paper; just be cautious when you pick your battles with it.
- Scolex. He behaves similarly to Pin and is about as dangerous as that implies, except that only his tail segment is vulnerable. As a result, you generally only get a window of about a second or so to damage him every time he jumps. Unlike other bosses like Rag Mega or Scolex's own variant Wormwood, Scolex does not have a lower HP value to account for his lengthy periods of near-invincibility, meaning that the fight usually drags on for far longer than it has to. Fortunately, he has one attack that leaves the tail vulnerable for a rather long time, but A.I. Roulette means there's no guarantee of him actually using it in place of his invulnerable head attack.
- Lokii, Loki's posthumous version, which is a Dual Boss. While a single Loki by himself is easy, Lokii is unbearingly tedious in comparison not because of how dangerous both halves' attacks can be, but because they both share Loki's health (Loki has 350 HP, whereas Lokii has a whopping 700 HP). The battle can become a Marathon Boss if your attack and/or fire rate aren't high enough, since you'll likely be focusing fire on one half before it teleports, at which point you'll go for the closest half... only for it to teleport again... and so on, so forth. Lastly, whereas both halves adopt the same attacks as the "alive" version of Loki, instead of Boom Flies, they summon Red Boom Flies, who instead of exploding on death, release bullets in an asterisk pattern. This means you can't rely on the flies' explosion to deal extra damage to them, forcing you to use the best of your abilities (and patience) to kill both halves for good.
- If two or more Lokis appear in the same room, the battle against them can also become tedious for the reasons above. The only saving grace would be the Boom Flies that can appear, allowing you to hit one or two Lokis with one explosion.
- The Krampus. Just by appearing, he will invalidate any Devil Room you might have earned on the level. He fights similar to The Fallen: his double spread bullet attack is just as difficult to avoid, even if you are running circles around him, and from Afterbirth onwards, he has the ability to rotate his Brimstone beams, which makes it even harder to avoid and can potentially result in taking damage twice from the same attack. Thankfully, he doesn't split into smaller versions of himself on defeat, and he can drop A Lump of Coal, which increases your shots' damage the farther they travel (although it might require Brimstone, Technology, or decently high range to get the most effective use of it).
- In Rebirth, he has a chance to drop the Head of Krampus, an item that unleashes a four-way brimstone that can clear rooms with small enemies easily and do serious damage to bosses. It ended up being so powerful on release, version 1.031 nerfed it from a three-room charge to a six-room charge, making it significantly less worthwhile unless you have no active items, or your current active item is bad. Afterbirth buffed it by letting the lasers spin around and potentially wipe everything in the room; however, this is not a guarantee, and this feature was removed in Afterbirth+.
- If you have the D6, both items can be rerolled for a random Devil Room item that you can then pick up for free, making the fight much more worthwhile.
- In Rebirth, to unlock access to the fight with Mega Satan, you typically need two key pieces, which are only obtained by fighting the angels Uriel and Gabriel, both of which can be found in Angel Rooms after beating ???/The Lamb, by bombing the Angel Statue(s) in the room. Both angels fit this trope, so if possible, make sure to use the Angel Room's item to your advantage.
- Uriel (the blue-scarfed angel) can be a bit tedious because of his fairly high healthnote . His attacks, which range from a single bullet spread and firing beams of light, are actually easy to telegraph and simple to avoid. The real danger comes from how he constantly chases you, shortening the space between you and him. Like with many other bosses, though, the later you find him on a run, the easier he becomes, depending on your current damage/fire rate and items.
- Gabriel (the red-scarfed angel) is even worse. He has even higher health than Urielnote , and while his bullet spread is easier to avoid than Uriel's (since it does not directly target you), he chases you faster and can fire beams of light in a cardinal cross pattern, leaving you with only a corner of the room to avoid it. Must we mention that the horizontal beams' hitboxes do not match the beams' position? He also has three attacks that are hard to telegraph due to the same initial animation: he can either fire beams of light in a diagonal cross pattern, use his bullet spread, or summon an Angelic Baby, a humanoid creature with wings that fires a triple bullet spread at you. Combined, these attacks make Gabriel a potentially more dangerous boss than Uriel.
- Mega Satan summons "fallen angel" versions of both of them during his fight, and both have more health than their original counterparts (Uriel has 450 HP, and Gabriel has 750 HP).
- Mom will be this to less experienced players. Dealing with the many mooks she can summon while dodging her stomps at the same time can prove to be a difficult task. It gets worse when she summons Clotties, Maws, and other projectile-using mooks. It doesn't help that rocks block the corners of the room and the doors have a chance of summoning her very fast and hard-to-dodge hand, leaving you with very little room to deal with your assailants. She's even worse in Rebirth since the stomps come out faster and the shadows warning of them are much harder to see.
- Her blue champion variant stomps slightly less, but spawns different kinds of enemies, including literal demonic spiders, Buttlickers and Keepers.
- The version that appears at the end of The Mausoleum in Repentance is even worse. The eyes that pop out fire off Brimstone Lasers and her stomps happen multiple times in quick succession (with a shockwave on the final stomp of any set, just for good measure, plus spawned enemies at the impact point). They also spawn many more foes, and they aren't restricted to being spawned at the doors either-
- Mom's Heart can also be this. At the start of the battle, there are Eyes waiting for you to make your move, and shooting lasers at your direction to make the heart harder to hit, and allowing it to retreat. When you get rid of them, you'll have to deal with the Heart's many Bullet Hell patterns, all the while fighting the many goddamned bats and demonic spiders that periodically appear during the battle when it retreats, including but not limited to more Eyes, Flesh Mobile Hosts, Walking Boils, Globins, Lumps, etc. While the bullet hell patterns aren't very difficult to avoid when you get the hang of them, as its health drops, the bullets become faster. And after losing 90% of its health, it stops spawning enemies and shoots four Brimstone lasers in a cross pattern that rotate around the room. With high damage and/or fire rate, the amount of mooks it'll spawn is minimal, and it might not be able to even shoot lasers. But the lower your stats are, the more difficult it'll become.
- It Lives, the upgraded version, can be even worse if you take your time, since the fetus can spawn Degraded Bosses from previous floors, such as Chub, Polycephalus and Teratoma.
- Great Gideon is generally not considered a hard boss by the standards of the more difficult Alternate Path in Repentance, but he is disliked for being tedious. Rather than being fought directly, he summons six waves of enemies that need to all be cleared in a 1x2 room, essentially making him like a miniature version of Greed Mode. This means that fights with him tend to be slow no matter how powerful a run is, with the only easy way out being to use a Chaos Card on him. Even so, Chaos Cards are very rare, and should the player have one, they might prefer saving it for a difficult final boss or superboss instead. The fight is also prone to bugs and RNG resulting in hard to avoid damage. To rub salt in the wound, he is the only boss that can show up in both variants of the alternate Chapter 2, so whether Mines or Ashpit generates, there is no guarantee that he will not show up in the run and bring it to a halt. His Ashpit variant is particularly obnoxious due to the sheer amount of Demonic Spiders found on the floor.
