Bio
The Brain of Cthulhu is a pre-Hardmode, Crimson-themed boss resembling a large, flying brain. It can be summoned when 3 Crimson Hearts are destroyed in a Crimson world, or when a player uses a Bloody Spine anywhere in The Crimson or Underground Crimson biome.
The Brain of Cthulhu has two stages. In the first, the Brain is invulnerable and teleports randomly around the player. 20 Creepers spawn along with the Brain and orbit the boss at high speed. Creepers do not respawn once they are killed. All Creepers must be destroyed first before the Brain of Cthulhu enters its second phase, where it becomes vulnerable to attack and can be killed.
Defeating the Brain of Cthulhu and its attendant Creepers is the only way to obtain Tissue Samples, and is one of the ways to obtain usable quantities of Crimtane Ore. Defeating the Brain of Cthulhu for the first time allows the Tavernkeep NPC to spawn.

Spawn Conditions

It can be summoned when 3 Crimson Hearts are destroyed in a Crimson world, or when a player uses a Bloody Spine anywhere in The Crimson or Underground Crimson biome.

Stratigies
Phase 1:
• The Brain cannot be attacked in this phase, only the Creepers can. The Brain will teleport to a spot in the arena, then slowly advance towards you. The Creepers will follow shortly after and will clump up with the brain for a few seconds before the Brain teleports again (and the Creepers follow). The idea is that the Brain will teleport behind you, which will make the Creepers fly into you, causing damage. Jump out of the way, either by using your platforms or with an extra jump, then attack the Creepers. Use piercing weapons to speed up the process. When a Creeper dies it can drop either Crimtane Ore or Tissue Sample.
Phase 2:
• When all of the Creepers are dead, the Brain will split, revealing a heart with an eye on the inside. The Brain becomes vulnerable to attacks and knockback during this phase. The Brain teleports much more frequently, often at unexpected angles, and will try to ram into you. The Brain only has 1000 / 1700 / 2167 health, so it can be killed fairly quickly. Keep using your platforms to jump out of the way, and use your strongest weapon to take down the Brain. If you have a weapon with high knockback, it will excel at dealing with the Brain, so much so that it's possible to stand in one location and attack it whenever it gets close.