Brain of Cthulhu

. The Brain of Cthulhu is a Boss. It is summoned with the Bloody Spine. It will also appear every time you shatter three Demon Hearts. The Brain of Cthulhu can only be summoned in the Crimson.

Behavior
There are two distinct phases in this boss battle. In the first phase, the Brain will be invincible and teleport around the room, surrounded by eyes that attempt to fly at the player, dealing damage. Each eye has its own health bar, and will drop Tissue Samples and hearts. When all the eyes are destroyed, the Brain is able to be damaged normally. In this second phase, the brain will continue to teleport, but will concentrate on ramming the player itself. In this second stage, the brain moves much faster than the first stage. In both stages, touching the Brain itself will deal high damage.

Trivia

 * The Brain of Cthulhu, like its counterpart the Eye of Cthulhu, is based on the character Cthulhu from the works of the author H.P. Lovecraft.