BRAINS!

BRAINS! is Challenge #27, added in Afterbirth. In this challenge, you play as ??? and start blindfolded, with 3 Bob's Brain and Thunder Thighs. Your goal is to defeat ???. Treasure Rooms do not spawn in this Challenge.

Difficulty

Bob's Brain is a difficult item to use, as it is not only easy to deal one full heart of self-damage when fighting enemies, it also leaves you exposed while waiting for the brains to respawn. Adding to the problem is that playing as ??? means you can't afford to make mistakes due to not being able to use red hearts. With no treasure rooms and having to reach all the way to The Chest, you will need all the skill and luck you can get to beat this challenge.

Strategy

Make sure to pick The Polaroid after the fight against Mom. If The Negative is chosen instead, ??? will not be teleported to The Chest after the Cathedral. You will not be able to fight ??? and the challenge will be over.
- You can only take The Polaroid, as The Negative won't spawn.
Try to space out your shots with Bob's Brain so you don't have to wait as long for one to spawn. If you can get a cycle going, it becomes easier to efficiently kill enemies, especially bosses, without taking as much damage.
Any method of damaging enemies besides Bob's Brain is incredibly helpful.
- Sharp Straw is incredibly useful as it can be used multiple times per room, deals high amounts of damage to any enemy including bosses, may drop half soul-hearts, and you do not have to aim to use it. For it to be obtained, however, you need to purchase Chaos from a shop, or survive until you reach The Chest.
- Like any blindfolded run, familiars are useful for this challenge. Not only can they safely extinguish fires (except Rotten Baby), they can help take care of weak or weakened enemies while the brains respawn. However, you do have to hold the firing keys to make them attack (excluding Succubus), increasing the risk of harming yourself by one of the brains. Most strong familiars are also exclusive to Devil Rooms, so you must maintain your health if you want them without putting your run at risk.
  - Most of Lilith's unlockables are especially valuable in this run; Incubus and Succubus are among the most powerful familiars, while Box of Friends can double any familiars you have. Taking the time to unlock these can be beneficial for this challenge.
  - Other good familiars aside from Incubus and Succubus include Demon Baby, who fires on its own, Lil Brimstone, who can hit multiple enemies per shot, and Rotten Baby, whose flies will home in onto enemies.
- The damaging trails from the Bob transformation or Headless Baby can be useful, allowing chasing enemies to be killed without the risk of taking damage from Bob's Brain. However, this method takes a lot of time and is useless against flying enemies.
- Buying The Candle or Red Candle from the shop can make this challenge a lot easier, since both do a lot of damage and can be used multiple times in a room.
- Orbitals, such as Cube of Meat and Sacrificial Dagger, can be a good source of damage. But make sure to not press the firing keys while your orbitals do damage, as you will harm yourself if you have at least one brain.
  - Once The Polaroid is obtained, orbitals start becoming more useful. Since the shield will always trigger from any damage, it will give you a little time to run into enemies and deal contact damage, preferably against weaker enemies to save the brains for stronger ones.
Pyromaniac and Host Hat make this challenge much easier, as ??? no longer takes damage from the brain's explosions.
Use Thunder Thighs to break rocks, as this can sometimes open a crawl space with items such as Pyromaniac.
- Also, keep an eye out for tinted rocks, as you can obtain valuable soul hearts, as well as pickups and items via Golden Chests. Thunder Thighs allows you to break them for free, so there is no reason to skip any of them. But it is not advised to pick up The Small Rock unless you have items that depend on your damage stat, as it lowers your already low speed.
Speed items help keep distance from chasing enemies, making it easier to avoid taking splash damage from a brain's explosion. Since Thunder Thighs slows you down, at least one or two Speed items are necessary to outrun most enemies.
Flying is very useful to give yourself more breathing room by preventing you from becoming cornered in a bad room layout, as well as negating the threat of spikes or creep.
IV - The Emperor can be extremely valuable, especially in the late game because it allows you to skip difficult floors like the Cathedral and the Chest and go straight to the boss, minimizing the amount of fighting required.
Keep an eye out for Libraries, since there are many good defensive or health-related items you can obtain, like Book of Revelations and Book of Shadows.
If damage via an enemy is unavoidable, collide with the enemy first and then blow it up with a brain while invincibility frames last. You will get hurt either way, but you will only lose half a heart instead of a full heart. However, this strategy does not work against Champion enemies (if it does two full hearts of damage, you are better off blowing yourself up instead) and enemies that naturally do one full heart of damage (like Chubbers), and you will always take a full heart of damage anyway starting from the Womb.

Notes

If you enter The Void once you kill Mom or Mom's Heart/It Lives, you can still collect the trophy by defeating Delirium. However, this is extremely unadvisable unless you have had a very good run up to the Mom fight and want an extra challenge.