Warlock

The Warlock is an NPC vendor that will spawn once the following conditions have been met:
 * There is an empty house.
 * The Eater of Worlds/Brain of Cthulhu has been defeated.

If the Warlock is killed, he will only respawn if the above conditions are met again. He uses skulls to defend himself.

Names
The Warlock can have the following names:
 * Azazel
 * Baphomet
 * Vaal
 * Dis
 * Nisroke
 * Sabnak

Trivia

 * Baphomet refers to the real life cult demon with the same name