Taking defense-boosting equipment off before dusk can prevent it from spawning randomly. The Eye of Cthulhu will only spawn randomly if a player has more than 10 defense.
It drops 3 / 7 50 up front, plus ores which can be sold as bars for twice (Demonite) or triple (Crimtane) that amount.
It now lets out a roar every time it charges. It no longer spawns Servants of Cthulhu, and has no defense, but now has increased contact damage. 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. Afterward, it charges at the player three times in succession, before repeating the cycle. A servant is spawned with the typical hit sound. During the first, it attempts to float directly above the player, while spawning 3–4 Servants of Cthulhu, which drop Hearts and Stars on death. The Eye of Cthulhu has two phases, and is able to fly through blocks in both of them. If they remain underground all night, the boss will not spawn at all. If the player is sufficiently far underground, the Eye of Cthulhu will not spawn until they return to the Surface. If spawning this way, its arrival is announced by the status message " You feel an evil presence watching you.".