Talk:Known Bugs And Glitches/@comment-201.78.41.96-20130621183055/@comment-91.144.201.56-20130623131423

As far as my memory serves...

Eye of Cthulhu can appear at random at night, as long as at least one player has 200+ max hp, and the Eye of Cthulhu has not already been beating on that world.

EDIT: "Also, it can randomly summon itself with a 33% chance each night if the following criteria are met:
 * At least one player in the game world has at least 200+ health.
 * There are at least four NPCs in the world. Note that the Old Man does count as one of these 4.
 * The Eye of Cthulhu has not already been defeated in the world."

~Eye of Cthulhu part of the Wiki