Brain of Cthulhu

. "A horrible chill goes down your spine..." "Screams echo around you..."

The Brain of Cthulhu is a Boss associated with the Crimson biome. It can be summoned by shattering three Crimson Hearts or through the use of a Bloody Spine.

Many Creepers spawn along with the brain, each of which has its own health bar and will drop items on death. These orbit the Brain of Cthulhu at high speed, and as long as even one survives, the Brain cannot be damaged in any way. The Brain has no means of creating new Creepers or replacing lost ones, however, and they drop Hearts at a higher rate than regular enemies. Once all Creepers are defeated, the Brain becomes susceptible to damage and attacks the player much more directly.

The Brain of Cthulhu is the Crimson counterpart to the Corruption's Eater of Worlds. Much like its cousin, fighting it is essential for progression, as the Brain and its attendant Creepers are the only source of the Tissue Samples and quantities of Crimtane Ore needed to craft advanced tools and armor.

First phase
Initially, the Brain of Cthulhu is invincible, but is surrounded by numerous relatively weak Creepers that attempt to ram the player. The Brain teleports around the player, drawing nearer before teleporting away again in a random direction. The Creepers do not teleport along with it, but are instead pulled between the player and the Brain in large, sweeping orbits. Once all Creepers are defeated, the brain enters its second phase.

Second phase
In the second phase, the Brain becomes damageable, continuing to teleport around but pursuing the player much more aggressively. Its speed increases and it will actually attempt to ram the player before moving to a new random location.

Tips

 * As Creepers drop Tissue Samples and Crimtane Ore fairly frequently, it's technically not necessary to defeat the Brain of Cthulhu to gain access to Crimson-tier equipment, only to kill a couple of Creepers and secure their drops.
 * Creepers have low individual health and are especially susceptible to the On Fire! and Frostburn debuffs, so weapons that inflict those can make quick work of them.
 * The Brain of Cthulhu is the only boss susceptible to knockback. Weapons with high knockback can keep both Creepers and the Brain from closing distance between teleports.
 * Unlike the Eater of Worlds, the Brain of Cthulhu doesn't run away and despawn if you leave the Crimson.

Trivia

 * The Brain of Cthulhu, along with the Eye of Cthulhu, is based on the character from the works of the author H.P. Lovecraft, Cthulhu, an unimaginably powerful being that defies comprehension. They don't capture the concept well since they can be killed, but how else would you have them?
 * Unlike the Eater of Worlds, the Eye of Cthulhu, and Skeletron, the Brain of Cthulhu does not have a respective Hardmode boss on PC, but Ocram may be it's counterpart for the console/mobile. (The others having The Destroyer, The Twins and Skeletron Prime respectively.)
 * The Brain of Cthulhu has the least HP out of all the bosses, with even less than the Eye of Cthulhu in its second form. However, if counting the health of its creepers, it has more health than King Slime.