Guide:Eye of Cthulhu strategies

Terrain and Gear


Like all Bosses, preparing for the fight is most probably the biggest factor in your success:

When fighting the Eye of Cthulhu, a strategy I've always found to work is to make an arena composed of a border of dirt or stone with wood platforms placed every 6 blocks inside it so that you can evade the Eye by either running, jumping or dropping. Don't forget to place some lighting around the arena since you definitely do not want to be fighting in the dark.

Arenas with walls on either side can limit your horizontal movement, but will also provide a backdrop for shuriken and bow users to easily pick up their expended ammo for reuse during the fight. Lots of platforms can provide greater mobility, but will seriously hinder the effectiveness of most ranged weapons as many types of ammo cannot travel through them. Balance is the key. Leaving gaps between platforms like shown in the example appears to allow for unhindered arrow flight.

Good Armor is recommended for this fight, because even though the boss doesn't hit very hard, its constant summoning of Servant of Cthulhu can be rather hard to dodge for the new/inexperienced player. If you start to get swarmed by too many, it may help to temporarily switch to a strong fast swinging item such as a pickaxe to get rid of them quickly since the summons have very little life. Ignoring them will be fatal since the damage they deal is not insignificant and they will keep swarming after you.

Finally, bring a batch of lesser healing potions. Two other helpful potions which are also easy to brew are the Regeneration Potion and the Ironskin Potion, and since they last a few minutes each you only need to make a couple or so.

Weapons
Due to all the servants this boss summons, weapons with a piercing attack are extremely useful. An effective weapon to take are shurikens, a stack or two is more than enough to defeat this boss with relative ease, other weapons to take would be a bow with Flaming Arrows/Unholy Arrows for the high damage. If you have the money to spare, grenades can be used. A Thorn Chakram is one of the most effective weapons against it, to the point where you can kill the Eye thrice in one night easily, or even four times in one night if you are skilled enough. It does more than double the shuriken's damage and comes back to you, so you don't have to worry about running out. However, acquiring the materials for the Chakram may be harder than the boss itself due to the dangers of the Underground Jungle. Because the boss is a flying type, melee weapons are limited in use since it is too dangerous to get close to it. No matter what the weapon of choice, weapons with higher damage per second are preferred. The greater your damage, the shorter the fight and the better your chances of survival.

First Phase
During this phase, the Eye will, for a large majority of the fight, float around above you, summoning Servants to fly towards you and kill you. It will still fly in roughly your direction so do not disregard it while you kill the summons.

A good strategy in this phase is to aim ranged weapons at the pupil of the Eye, since that is where it spawns the Servants. That way, you can kill the servant and damage the Eye. If you stand directly below the Eye and aim straight up with a piercing weapon, after a few seconds your projectile will fall back down and hit the Eye again. A side option is to stand still while it spawns its Servants and throw Shurikens at high amounts at it, this will instantly kill any Servant it spawns and leave you completely safe. When it stops spawning Servants, run away from it since it can only go so far in one charge and its turn is horrible while charging. Rinse and repeat and the first phase should go down easy.

Second Phase
For the last half of the fight, the boss turns its iris and pupil into a mouth. Make sure to take advantage of its transformation sequence as much as possible, since it just spins in place for a few moments and you can still damage it. It moves slightly faster and deals more damage when it hits you but it also has less defense. Since it is not summoning anymore this time it will simply keep rushing at you. It'll charge you 3 times, and then wait a few seconds during which you can nuke him. In these few seconds, you have to hit it with your hardest hitting weapon. For newer characters who haven't made it to the Gold/Silver stage, Shurikens are your best bet.

Survival
Like the Eater of Worlds, the Eye of Cthulhu will flee if the player dies while fighting him. It will also flee if the player fails to defeat it before early dawn (about 4:30am, if you're wearing a watch). The best way to avoid this is, like the other methods described above, a matter of preparation. Start the fight early after sundown, take lots of potions with you, and wear the best gear available to you.