The Eye of Cthulhu has two phases, and is able to fly through blocks in both of them. During the first, it attempts to float directly above the player, while spawning 3–4 Servant of CthulhuServants of Cthulhu, which drop Hearts and Stars on death. A servant is spawned with the typical hit sound . Afterward, it charges at the player three times in succession, before repeating the cycle.
When the Eye of Cthulhu falls below 50% / 65% health (1,400 / 2,366 / 3,016), it transforms into its second form (shedding its iris into a mouth), which rams the player more aggressively three times, then hangs in the air for a period. It no longer spawns Servants of Cthulhu, and has no defense, but now has increased contact damage. It now lets out a roar every time it charges.
In Expert Mode, the boss spawns more Servants of Cthulhu than normal, as well as 4–5 servants upon transforming. In the second phase, it will gain an additional powerful rapid chain dash attack, during which it lets out a higher-pitched roar every time it dashes. These dashes become faster as the Eye of Cthulhu's life decreases, and it can dash nearly continuously when close to death.
If the Eye of Cthulhu is not defeated by dawn (4:30 AM), if all players die, or if the Eye of Cthulhu goes too far off-screen, it will despawn.
