Guide:Brain of Cthulhu strategies

"A horrible chill goes down your spine..."

The Brain of Cthulhu is Pre-Hardmode boss. It's The Crimson counterpart of Eater of Worlds.

Spawn Conditions
The Brain of Cthulhu can be spawned by fulfilling one of these conditions: It must then be defeated within the Crimson: getting out of it will make it retreat and despawn.
 * Smash three.
 * Use.

The Fight
Brain of Cthulhu has 2 phases, with the latter starting after all Creepers have been dealt with.

First Phase
The Brain cannot be attacked in this phase, only the Creepers can. The Brain will teleport to a spot in the arena, then slowly advance towards you. The Creepers will follow shortly after, and will clump up with the brain for a few seconds, before the Brain teleports again and the Creepers will follow. The idea is that the Brain will teleport behind you, which will make the Creepers to fly into you, causing damage. Jump out of the way, either by using your platforms or with an Accessory like the Cloud in a Bottle, then attack the Creepers. Use piercing weapons to speed up the process. When a Creeper dies it can drop either Crimtane Ore or Tissue Sample.

Second Phase
When all of the Creepers are dead, the Brain will split, revealing a heart with an eye on the inside. In this phase, the Brain will teleport much more frequently, often at a funny angle, and will try to ram into you. He only has 1000 health, the lowest of all the bosses, so he can be killed fairly quickly. Stay calm, and keep using your platforms to jump out of the way. Use a single-targeting weapon to take down the brain, as piercing weapons are less effective against singular targets. If you have a weapon with a high knockback value like a Spear, it will excel at dealing with the Brain, so much so that it's possible to stand in one location and stab it whenever it gets close. When the Brain dies it will drop a large amount of Crimtane Ore, and Cthulhu will be a little less intelligent.

Expert Mode
The Creepers are much more aggressive. They will actively try to fly into you, even ignoring the Brain if it means an opportunity to land an extra hit or two. They can also inflict a large variety of debuffs; more than any enemy in the game. They can range from being completely unable to use Magic weapons to having your vision darkened.

During the Second Phase, the Brain will spawn clones of itself around the player. They serve as decoys, and while they cannot be attacked they can confuse the player as to which one is the real Brain. They start off as barely visible but as the Brain loses more health the clones will become more opaque. At low health the clones will be completely visible. The Brain will also become faster as it loses health, too. Life-draining debuffs such as On Fire and Frostburn, or a Hunter Potion will help distinguish them. Additionally, summoned Minions will always target the correct copy. Using your Bone Javelin or Spiky Balls if you have platforms in your arena will also help significantly.

Preface
The Brain of Cthulhu can only be spawned and fought in the Crimson. As such, it would be best to create an artificial crimson area to fight in. Alternatively, you can find naturally occurring Crimson and create an "arena" there. However, if you plan to create a floating arena, you may have to hollow out a large section of the Crimson to do it, as going too far above to it will be considered exiting it, causing the Brain of Cthulhu to despawn.

Remember that explosives such as and, and Eye of Cthulhu are your best friend. Explosives can destroy, while the Eye, when defeated, drops. You can use these to create small artificial floating islands made of Evil grass and Crmstone, which can help the boss to not despawn if you fly too high. This hint is helpful to all Biome-inclusive bosses that you will encounter later, by using biome-respective materials.

Building a small artifical island requires that you place a tower of blocks or platforms, and then place evil blocks when high enough. It's recommended to place these blocks as soon as you hear the Forest music, because at that point, Crimson ends. After placing enough blocks to make it corrupted, proceed to extend the arena with your own desired design, or use one of those below.

Arena Designs

 * You'll want to set up a long platform in The Crimson, because it can only be summoned there. It should be high enough so ground enemies can't jump up to you, but low enough that you don't accidentally go high enough to make it despawn. An arena the size of your screen is preferred, since you can see the whole area in the middle, and enemies can't go jumping in.
 * Since the Brain of Cthulhu spawns as soon as you smash a third Crimson Heart, you're likely to be in tight quarters when the attack begins. This can lead to you to being swarmed by the Creepers and get overwhelmed. This can be avoided by preparing the chasm's main chamber as an arena beforehand, and choosing which Hearts to break first:
 * For the first two, pick the least convenient hearts (distant, above the main chamber, underwater, etc).
 * For the third, pick the closest below the main chamber, and reshape its tunnel to guide a Bomb down to the Heart from the high end of the tunnel (you can test the route with Glowsticks).
 * Then, you can toss the bomb and leap for your arena while it falls.
 * You can "box" the main chamber, by simply putting up walls and ceilings in the big chasm the crimson usually forms.

Gearing up
It is recommended to have at least 200 Life, which requires 5 : if you've done some spelunking you're bound to have come across this many.

You're going to need at least Iron or Lead armor. Gold armor or Platinum armor is a great defensive choice with high defensive values for this point in the game, but considering the rarity of their respective ores it may not be worth it. For those playing during Halloween (or have planted some ), you can harvest for Pumpkin armor which has the same defense value as Iron's, but it trades off the +2 defense bonus with a more helpful 10% damage bonus.

Weapons
For melee users:
 * Blood Butcherer.png Any large sword, such as the Blood Butcherer will prove effective against the Creepers. The Falcon Blade is useful for the Brain of Cthulhu's second phase, as its rapid speed, somewhat high damage, and decent knockback will keep it at bay. The Katana, sold from the Travelling Merchant, is a fast sword with decent knockback and a high critical rate. If you're able to obtain them, the Muramasa from the Dungeon or the Blade of Grass from the Jungle are both extremely good.
 * The Rotted Fork.png A Spear is a great weapon against the Brain of Cthulhu, especially during the second stage. Suggested options are the Trident and The Rotted Fork.
 * A Flail of some kind is beneficial for taking out the Creepers; the easiest to obtain would be the, but this will require you to make another world with The Corruption in it, as it cannot be acquired in a Crimson world. You could instead try to obtain the , a rarely dropped by , but unlike the previously mentioned flail, it cannot pierce.

For ranged users:
 * is the most powerful bow at this stage. You can combine it with, which greatly help to kill the swarm of Creepers. However, you can also use the as a cheaper alternative; the  debuff will be helpful during the second stage.
 * As can be obtained very easily (as it's a guaranteed first-time loot from the Hearts), it's a good weapon to use against the Brain. The  that spawn with it should be sufficient, but you can craft (or buy), which deal sligtly more damage.

For magic users you want a minimum of 100 Mana, and 6-8 Lesser Mana Potions. The Water Bolt and Crimson Rod are good choices that are obtained fairly easily which benefit from fighting the Brain in an enclosed area. The Emerald Staff and Diamond Staff are very easy to make and you'll find their piercing ability (especially that of the Diamond Staff) to excel at dealing with the Creepers. If possible, you can also get Jungle armor to boost your damage and Mana efficiency. If you're willing to make a quick detour to a Corruption world, Vilethorn works fantastically against the Creepers and is a great weapon in general. One final choice, is a full set of Meteor armor with the Space Gun; with the full set, the Space Gun will not consume any Mana, allowing you to spray and pray at the brain; the piercing ability of the Space Gun will clear out the Creepers fairly easily. However, this setup requires that a meteor has landed, which is an event that requires you have a Tungsten Pickaxe at the minimum or explosives to collect the meteor's ore.

Exclusive Summoner users will have very limited options during this fight; your best option is the Hornet Staff, which is crafted from Bee Wax, a drop from the Queen Bee. Alternatively there is the Slime Staff but this is a 1:10000 chance drop, so it's likely you will not get it. At this stage of the game, it's better to use a summoning weapon alongside another class setup, unless confident in your skills.

Throwing users can use Shurikens and Throwing Knifes as basic weapons. Poisoned Knifes can be crafted using Vicious Powder and Throwing Knives and deal a little extra damage. Grenades are great choices for dealing with the Creepers but you are advised to watch out for the blast radius, as you will take damage. Molotov Cocktails also work great because of the splash damage and the fire that hits multiple times keep the brain away in its second stage.

Multiplayer
If playing with someone, have one melee player who has The Rotted Fork or another spear to hit the Creepers in the first stage, and have a ranged player off to the side with The Undertaker, a Gold/Platinum bow, or a Gem Staff. In the second stage, the melee player should use The Rotted Fork/Spear to keep the Brain from doing massive damage, and the ranged player should keep shooting it. If you have more than 2 people, have 1 melee and extra ranged players.

Potions
6-8 Lesser Healing Potions will keep you going during the fight. As stated above, you should also get some Lesser Mana Potions if you're a magic-using player. For buffs, the Ironskin Potion, the Swiftness Potion and the Regeneration Potion will do you well. You should try to get the Well Fed Buff in some way; you can get this from Cooked Fish or Pumpkin Pie.

Accessories
The Cloud in a Bottle will give you a double-jump ability which will greatly help with evasion. Look out for the improved versions, such as the Tsunami in a Bottle, the Blizzard in a Bottle or the Sandstorm in a Bottle.

The Hermes Boots will increase your speed and aid greatly in evasion. You can upgrade them to the Spectre Boots for the added bonus of a few seconds of flight, but this requires the Goblin Tinkerer, which the player may not have yet.

The Band of Regeneration is a decent accessory which will slowly regenerate your life; it equates to one heart restored every 40 seconds. Not terribly useful but it's suggested if you have a slot you need to fill.

The Anklet of the Wind gives a basic 10% speed boost, which will help out with evasion. You can replace it with the Aglet which is much easier to find but only offers a 5% speed boost.

The Frog Leg will give you improved jumping abilities, including increased height and automatic jumping but it can only be found by fishing, with an incredibly rare 1:500 chance to get it.

If one is playing in Expert mode, the Shield of Cthulhu is a great choice for quick evasion, and extra damage in the Brain's second phase.