The Eye of Cthulhu is a boss mob from the Terraria Idea Pack. It is summoned by the Eye of Cthulhu Summoner, which is crafted with a Fake Eye and a Gold Ingot in a shapeless recipe. Eyes of Cthulhu can also spawn with a 1/20 chance at night when the player has obtained at least one Diamond.
The Eye of Cthulhu flies about the land, occasionally plunging down to attack the player. Every 10 seconds, it has a 5/6 chance to spawn 8 Servants of Cthulhu, which attack by swarming the player. When the Eye is lowered down to half health, its iris splits open and reveals a mouth with fangs. It does more damage and is faster in this stage, but the Servants stop spawning. If hit outside the mouth, it will only take 1 damage.