The brain of Cthulhu is a highly dangerous flying demon brain. It can teleport randomly and has several demon eyes around it at all times, which orbit it like a shield. In fact, it seems to be impossible to hurt until you kill every last one, at which part a hole opens in it's head, revealing a heart with an eye. At that point, it can be hurt, but it rams you and teleports even more. It can also pass through solid objects with impunity. It is advised to simply release a horde of zombies on it, thus killing two birds with one stone.