Eye of Cthulhu

"You feel an evil presence watching you..."

The Eye of Cthulhu (not to be confused with the Yoyo of the same name) will be the first Boss a player will generally encounter, as it spawns automatically when a relatively early level of game advancement is achieved. It is considered the second easiest Boss in the game (after the King Slime), though it still presents a challenge to newer players.

Spawn
The Eye of Cthulhu can be summoned manually using a Suspicious Looking Eye at Night. It also has a 1 in 3 chance of spawning automatically each night once the following conditions are met:


 * At least one player in the world has at least 200 life and more than 10 defense.
 * At least three Town NPCs are acquired.
 * The Eye of Cthulhu has not yet been defeated in the current world.

Its approach is signaled with the message: "You feel an evil presence watching you..." Within 20-40 seconds of this message, the Eye of Cthulhu will appear and begin attacking the player. If the Eye is not defeated by dawn, or if all players die or run away while fighting it, it despawns.

Behavior
The Eye of Cthulhu looks like an enormous Demon Eye. Like most bosses, it travels through all blocks.

The Eye of Cthulhu has two phases. During the first, he spawns Servants of Cthulhu while floating around the player, which drop hearts and stars on death. After spawning a round of those, he flies at the player 3 times.

In Expert mode he spawns more servants than normal.

When the Eye falls below half health (1400), it transforms into its second form, which rams the player more aggressively 3 times, then hangs in the air for a period. It no longer spawns Servants, and has lowered defense. In Expert Mode, it will also spawn 4-5 Servants upon transforming.

The second form has another attack exclusive to Expert Mode, which is an empowered version of the dash, which also increases it's defense by a large margin. The lower its health gets, the more frequently it dashes madly at the player, often killing newer players before they can finally defeat the Eye.

In Expert Mode, the Eye of Cthulhu will do a fast chain dash in its second phase, using the attack more often the lower health it has. This can lead to it dashing almost continually at very low health, making it especially difficult for players in the early game to finish it off.

Tips

 * The Eye of Cthulhu drops either Demonite Ore or Crimtane Ore. Game-advancing tools at that tier also require Shadow Scales or Tissue Samples respectively, which the Eye doesn't drop, so players will have to fight the Eater of Worlds or Brain of Cthulhu to progress.
 * Due to the ease of crafting its summoning item and relatively low difficulty, farming the Eye of Cthulhu is one of the most effective ways of making money prior to Hardmode.
 * The Eye of Cthulhu will only spawn if you have 10 or more defense. Taking defense-boosting equipment off before sundown can prevent it from spawning randomly.
 * When the Eye of Cthulhu is changing into its second form, it stops moving and spins for a couple seconds, similarly to Ocram, leaving an opening to deal damage without it attacking back.
 * The Eye looks at the player it will follow, which can be helpful information in multiplayer.
 * In the Eye's Second Form, it cannot shoot its Servants, so it's best to use a Bow or ranged weapon against its second stage.
 * Due to the value of Crimtane Ore being 1 silver coin more than each Demonite ore the average drop value is slightly more in crimson worlds than corruption worlds(846.5 Silver Coins vs 790.76 Silver Coins).
 * If you manage to get the Slimy Saddle you can jump on the eye and kill it in this manner.
 * If you also manage to defeat Skeletron (unlikely) and you have the Book of Skulls, you can defeat the eye easily in a matter of seconds.
 * In Expert Mode, make sure you have boots that increase your running speed, such as Hermes Boots, so you can more easily dodge its faster charge attack.

Trivia

 * Cthulhu is an entity from the works of writer H.P. Lovecraft, first appearing in his short story The Call of Cthulhu. Cthulhu is described as a slumbering Elder god who will destroy all living things should he ever awaken.
 * Sometimes NPCs will mention sensing something evil watching them when you meet the requirements to battle the Eye of Cthulhu.
 * In the Mobile Version, the battle music is Boss 4 instead of Boss 1.
 * The endgame boss, the Moon Lord, spawns enemies called 'True Eye of Cthulhu'. This suggests that this Eye of Cthulhu isn't actually Cthulhu's eye.

History
Œil de Cthulhu Eye of Cthulhu Eye of Cthulhu Глаз Ктулху 克蘇魯之眼