The Eye of Cthulhu (often abbreviated as EoC) can be summoned by using a Suspicious Looking Eye at night. Alternatively, it can randomly spawn with a 33% chance each night if the following criteria are met:
- At least one player in the world has at least 200+ HP.
- There are at least four NPCs in the world. Note that the Old Man counts as one of these.
- The Eye of Cthulhu has not already been defeated in the world.
If these conditions are met, the player may get the message, "You feel an evil presence watching you...", which means that the Eye will spawn soon. After about 15-30 seconds the message, "The Eye of Cthulhu has awoken!" will appear and the boss will promptly start to attack the player. However, if the player isn't ready to fight the Eye of Cthulhu, the battle can be canceled by simply exiting and restarting the world, or alternatively restarting the game.
The Eye of Cthulhu has two phases that it goes through as it battles with the player. The first phase, a giant eye, has 15 attack power and 12 defense, while the second phase, a giant eye with a gaping jaw in place of its lens, has a 23 attack power; however, it has no defense. A good weapon to use during the first phase is the Starfury: It being a broadsword means you are able to fend off The Servants Of Cthulhu and use its ranged ability to fight Cthulhu. Another weapon suggestion for the first phase would be the Space Gun. (It is advised that the player has full Meteor Armor as this makes the Space Gun use 0 Mana.) The Crimson Rod can also be useful when the Eye is simply hovering, as it will kill the Servants easily and allow the player to focus on the Eye. It can also deal a good bit of damage when the Eye is switching phases as it will stay stationary when doing so.
As the Eye of Cthulhu can only summon itself if your max HP is 200 or more, you can delay its arrival by holding onto any Life Crystals that will increase your max HP to 200 or more until you feel that you're ready. That way, you'll be able to wait until you can craft Gold Armor and a Gold Bow. However, if you're not patient enough to want to grind for gold-tier equipment, then you should at least have Iron Armor or better, an Iron Broadsword or better, and, most importantly, some sort of ranged weapon, such as Shuriken, Throwing Knives, or a bow (preferably Iron or stronger) with Flaming Arrows. Also, bring along any Lesser Healing Potions in case you need to heal. If possible, get Glowing Mushrooms for Healing Potions instead.
If you are feeling like just rushing in the game, and are skillful or lucky enough, you can make a Topaz Staff, get some Fallen Stars for extra mana, and get some Iron Armor. With 160 or 200 health, and Healing potions, you can beat the eye with just dodging skills and a nice aim.
The following consumables may also be of some help:
- Ironskin Potion: This will increase your defense by 8 for five minutes, allowing you to take up to four less damage from the Eye of Cthulhu's attacks.
- Thorns Potion: For two minutes, enemies will take half of the damage that you take. This can make the battle go a bit quicker, though you'll probably want to try to avoid the Eye's attacks instead, especially during phase two.
- Archery Potion: For four minutes, the damage dealt by your bow & arrow increases by 20%, which will help decrease the time of the battle greatly.
- Regeneration Potion: For two minutes, your health regeneration is augmented, allowing you to recover more lost health in a faster period of time.
- If you have explored enough, and you are better with melee weapons in general, a Gravitation Potion with a silver or golden Broadsword may also be of use.
- A Mana Potion may be of use if you have magic items such as crimson rod or aqua scepter, (If you have found it in a chest or a friend has gifted it to you.
- Shurikens: These weapons can be thrown rapidly and can penetrate through enemies, meaning that these can not only kill Servants of Cthulhu in one hit (thanks to their attack power of 10), but they'll also go on to damage the Eye itself. Although they only deal 4 damage to the Eye's 1st phase, due to their piercing mechanics, they'll often damage the Eye more than once, making them an ideal weapon. They're pretty easy to obtain as well, since not only are they commonly found in pots, but they can be purchased from the Merchant at any time for only 20 copper each. Throwing them straight in the iris of the Eye will hurt the servants as well.
- Throwing Knives: Although they are a bit harder to get than Shurikens (they're also common in pots, though the Merchant will also sell them during a Blood Moon for 50 copper each), they deal a bit more damage, and can likewise be thrown rapidly and penetrate enemies. They deal 6 damage to the Eye of Cthulhu's 1st phase and can hit the Eye more than once per throw. However, if you're skilled (or lucky) enough to have access to Vile Powder (which is crafted with Vile Mushrooms from the Corruption), you can use that to upgrade your Throwing Knives into Poisoned Knives, which deal 7 damage to the Eye's 1st phase, and can even poison it, inflicting even more damage in the process.
- Bow & Arrow: Although you cannot fire a bow and arrow as rapidly as you can throw Shurikens or Throwing Knives, it's on here due to its potentially high damage output. A Golden Bow with Flaming Arrows deals 17 damage, which means that it'll deal 11 damage to the Eye's 1st phase. While Flaming Arrows cannot penetrate enemies like Shuriken or Throwing Knives can, it does have a chance of setting enemies on fire, damaging the Eye even further. On the other hand, a Golden Bow with Unholy Arrows (which are made out of normal arrows and Worm Teeth, which are dropped from Devourers) deals 19 damage (13 damage to the Eye's 1st phase), and can penetrate enemies like Shuriken and Throwing Knives can, though it'll travel too fast to damage the Eye multiple times.
- Musket: If you have Silver Bullets, this could be of use. Regular Musket Balls work as well, but you should have Golden or Silver Armor and Lesser Healing Potions or Healing Potions, as its very slow speed can make it difficult to do consistent damage. With Musket Balls it does 30 damage in the second phase, and 18 in the first.
- Rare Weapons: Most rare weapons you find in chests in the game will help you a lot. For example you can use an Enchanted Boomerang with your armor (Gold or better) and Healing Potions you should be able to defeat the eye easily. If not, a wooden boomerang will do, for it can take out the servants.
- Bone Javelin is also a well-used weapon with this fight and can only be obtained in version 220.127.116.11
- A Staff (sapphire or topaz recommended) is an optional magic weapon for the slightly more resourceful or experienced players.
Mobility in all directions is important in avoiding the Eye of Cthulhu's attacks, and chances are that you won't have access to such items as Rocket Boots or Hermes Boots. Due to the player's limited jumping skills, it is strongly advised that you build a boss arena that consists of multiple rows of wooden platforms. Finally, the arena should have some tall walls to keep other enemies from entering the arena, though, a ceiling isn't required. With no ceiling, Shurikens, Throwing Knives, and Arrows that are thrown upwards would fall back into the arena, and can still damage the Eye of Cthulhu during the descent. Keep in mind that the EoC and its Servants are immune to Spikes.
Try to have an open-roofed arena because a falling star can do 1000 damage to the Eye of Cthulhu!
Also remember to light the arena with torches, as the battle can only take place at nighttime.
The Eye of Cthulhu can only be summoned during night-time and will disappear without dropping any loot if the player does not kill it before daytime. Therefore, the best time to summon this monster would be soon after nightfall. That way, you'll have pretty much all night to defeat it.
The Eye of Cthulhu will try to hover high above the player and shoot out a Servant of Cthulhu every couple of seconds from the iris. The Servants of Cthulhu each have an attack of 12, but only 8 HP, which is low enough for them to die from one Shuriken. While the Eye is summoning Servants, you should be aiming for the pupil, as that's where the Servants will spawn from. If any stray Servants do get too close, then a Broadsword is useful for getting them out of your hair.
After four to six Servants of Cthulhu have been launched, the Eye of Cthulhu will start to dive towards the player three times. It has an attack power of 15, which can be damaging if care is not taken. Still, players should try to avoid these dive attacks whenever possible, changing to a higher or lower level if need be. Note that it's possible to lead the Eye's dive attacks by jumping before it attacks.
Once the Eye of Cthulhu reaches 1400 HP or below, it'll start to spin around violently, shedding its iris "covering" (and lowering its defense to 0) to reveal a jaw full of sharp teeth, and setting the stage for phase 2 of the battle. While this happens, it is recommended to damage it as much as you can, due to lack of movement and retaliation. While the Eye no longer spawns Servants of Cthulhu during this phase, it hovers closer to the player to ensure that its lunge attacks (which now do 23 damage) are more accurate. It also attacks quicker, making it more difficult to lead its attacks.
However, while the Eye of Cthulhu's speed is usually faster than the player, its acceleration and deceleration are rather poor. A clever player can exploit this by running in one direction, causing the Eye to give chase, then immediately stopping and running in the other direction, causing the Eye to drift away as it struggles to keep up with the player.
At the beginning of phase 2, the Eye of Cthulhu will release severals Servant of Cthulhus in an addition to his transformation which may interfere with the player's battle. While this happens, it is recommended to get rid of the stray servants first before dealing with the boss itself. It will still lunge towards the player as it was in normal mode regularly.
When damaged enough, the Eye will follow up its lunge attack by supercharging towards the player three times--Which is essentially a much faster variant to its lunge attack. As it continues to get damaged, the Eye will slowly replace its lunge attack and supercharges more frequently up to six times in a row in a more shorter interval and ultimately will continuously supercharge at the target at very low health until either himself or the player dies.
Expert mode strategy
One of the easiest ways to defeat the Eye of Cthulhu, and maybe the safest way, is to build a track for your minecart. This track must be at least 500 tracks long and the ends must have the bumping pieces. You can use any ranged weapons, everything to attack the Eye of Cthulhu from a safe distance. You don't need potions or anything else because if you use this strategy, you can win without ever been damaged.
To defeat the Eye of Cthulhu, you need to get in your minecart and travel in one direction. Always keep a safe distance to avoid being hit by the Eye of Cthulhu's supercharges. While you travel, you need to use your ranged weapons. If you keep enough distance, you can win without ever been damaged. If you reached the end of the track, you need to use the bumper piece and try to pass the Eye of Cthulhu without touching it. Then repeat this strategy.
- If a player uses the Suspicious Looking Eye after they have received the, "You feel an evil presence watching you..." message (provided the message was received at night), an Eye of Cthulhu will spawn and shortly after another Eye of Cthulhu will appear, thus leaving the player to fight two bosses at the same time.
- If the Eye of Cthulhu is hit by a falling star, it will take 1000 damage, minus its current phase's defense.
- A player using Hermes Boots or Lightning Boots may be able to out-run the Eye of Cthulhu.
- Late in the game, the Eye of Cthulhu can be an easy source of gold coins, because it can be defeated easily (endgame players can defeat him in mere seconds) and the Demonite or Crimtane dropped from it can be sold for a lot of money.
- The Eye of Cthulhu will drop either Demonite or Crimtane ore depending on whether Corruption or Crimson was selected in the world creation.
- The Eye of Cthulhu will most likely be the players' first boss to fight unless the player is foolish enough to try and attack Skeletron on his/her first night.
- If a player uses the Suspicious Looking Eye while fighting the Eye of Cthulhu on a Pre-Hardmode world, the player will Simply explode, and the Eyes of Cthulhu will despawn. If done in a Hardmode world, the player will not explode on the use of the 2nd suspicious looking eye and will be forced to fight 2 Eyes of Cthulhu.
- In mobile if you try to summon two Eye of Cthulhus with 2 Suspicious Looking Eyes one will be summoned, and the other one will either disappear or stay.
- If the player is unlucky, the Eye of Cthulhu will spawn on the first night, making it hard for the player to react when it spawns due to the low amount of armor/weapons.
- The current mobile version now plays the Boss 1 music and also spawns Servants of Cthulhu. Prior to this, the music played would be the Boss 4 music (played during the battle with Queen Bee and Ocram) and would fail to summon servants, despite them existing in the game.
- King Slime may be encountered before this boss, if the player spends a lot of time near the ends of the map.
- The Eye of Cthulhu is named after the fictional extraterrestrial entity, Cthulhu, created by horror author H. P. Lovecraft.
- The correct pronunciation of Cthulhu has long been debated. KAH-THOO-LOO and CHA-THOO-LAH are two commonly argued pronunciations. In reality, Lovecraft intended the name to be unpronounceable, as the creature pre-dated the English language.
- In patch 1.0.3, during multiplayer, if you pulled out a Suspicious Looking Eye, an Eye of Cthulhu would spawn and your Suspicious Looking Eye would not be taken away.
- A boss resembling the Eye of Cthulhu, known as Monoculus, was introduced to the FPS game Team Fortress 2, around Halloween, 2011. Monoculus appeared as a large eyeball shooting smaller eyeball projectiles in a similar manner to the Eye of Cthulhu.
- The first form of the Eye of Cthulhu seems to be a larger version of the Demon Eyes, which must be killed to gain Lenses to craft the Suspicious Looking Eye.
- There is a Yoyo weapon named after the Eye of Cthulhu.
- If The Eye of Cthulhu is summoned during a Blood Moon using a Suspicious Looking Eye the Dryad may not spawn.
- If The Eye of Cthulhu is killed too quickly, the defeat message will not show and loot will not spawn. (Mobile version)
- If you lead the Eye of Cthulhu up to the very top of the map, then drop down rapidly enough for the Eye to leave your screen, it may despawn.
- Attempting to use a Suspicious Looking Eye before night would make the Suspicious Looking Eye disappear without spawning the Eye of Cthulhu. (Fixed)
- Now drops Eye of Cthulhu Mask.
- Now drops Crimtane Ore instead of Demonite if your world has the Crimson in it.
- Now drops Binoculars.
- Now drops Eye of Cthulhu Trophy.
- Doesn't drop Heart Crystals anymore.
- Added to the game.