Guide:Brain of Cthulhu strategies

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

The Brain of Cthulhu is a 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 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 extra jump, then attack the Creepers. Use piercing weapons to speed up the process. When a Creeper dies it can drop either or.

Second Phase
When all of the Creepers are dead, the Brain will split, revealing a Heart with an Eye on the inside. The Brain teleports much more frequently, often at unexpected angles, and will try to ram into you. He only has 1000 health, so he can be killed fairly quickly. Keep using your platforms to jump out of the way. Use your strongest weapon to take down the Brain. If you have a weapon with high knockback, it will excel at dealing with the Brain, so much so that it's possible to stand in one location and attack it whenever it gets close.

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:
 * : reverses the movement buttons;
 * : saps 2 health per second;
 * : stops health regeneration;
 * : reduces vision;
 * : makes you unable to cast any Magic weapons;
 * : reduces your Defense by half;
 * : reduces Melee damage and Attack speed, Movement speed and Defense by 4.

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. 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. 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. Unlike the Lunatic Cultist clones, the Brain of Cthulhu clones do not appear on the map, making it trivial to tell which direction the real boss is coming from.

Terrain Preparation
Your arena will have to be built in The Crimson, because it can only be summoned there. Since the Brain of Cthulhu spawns as soon as you smash a third Crimson Heart, you're likely to be in a very enclosed area when the fight 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 to the main chamber, toss a Bomb or another explosive and quickly go to your arena while it falls.

If summoned with a Bloody Spine, then the arena can simply be made in the Surface, however do not make it very tall, as jumping too far above it will be considered exiting the Crimson, causing the Brain of Cthulhu to despawn.

Gearing up
It is recommended to have at least 200 Life and 100 Mana, which requires 5 and : if you've done some spelunking you're bound to have come across this many.

or is recommended if you are willing to mine enough of their respective ores. You can get by killing enough Creepers without necessarily defeating the Brain itself. or are slightly riskier, but ultimately also viable options, especially if you are confident in your dodging abilities.

It is possible to kill the Brain of Cthulhu with just or, but the fight will be a bit more dangerous. is another viable option, rewarding slightly less defense than Iron / Lead, but increasing your damage output, which can ensure the fight is completed quickly.

Accessories with Menacing or Warding modifiers will be most efficient here if you have them, but are not required.

Weapons
For Melee users:
 * Any large sword, such as the, will prove effective against the Creepers. The 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 , sold from the , is a fast sword with decent knockback and a high critical rate.
 * A spear is a great weapon against the Brain of Cthulhu, especially during the second stage. Suggested options are the and.
 * A flail of some kind is beneficial for taking out the Creepers; the easiest to obtain would be the (craftable from a, which can be found in  located underground). Even more effective would be , which would require killing a few Creepers (but not necessarily the Brain itself). You could instead try to obtain the , rarely dropped by , but unlike the previously mentioned flail, it cannot pierce.
 * A yoyo would be useful against the Brain in its second stage; the is a great choice at this point, although the  (available from the Traveling Merchant) is also a good option if you can get one, having higher damage but quite low knockback.

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 as a slightly cheaper alternative; the  debuff will be helpful during the second stage. Also, you can use  as a fallback, with their  debuff also helping 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 slightly more damage. Alternatively, once you obtain , you can gain access to the , who can provide you with a , which is effective against the Creepers if used with Silver or Tungsten bullets due to its rate of fire, but ineffective against the Brain in the second phase due to its low damage.
 * Another gun that you might have acquired at this point is the Boomstick. It may be useful in taking out the creepers, as they have low individual health and there are many of them.

For Magic users:


 * The is a great support weapon that can easily be obtained through Crimson Hearts.
 * A (or, failing that, a ) is easy to make, and with its decent damage and piercing ability, it is particularly effective against the Creepers. A  or  would work as well or better, but (being harder to obtain) are not worth going out of your way for.
 * If you're willing to make a quick detour to a Corruption world, the works fantastically against the Creepers and is a great weapon in general.
 * If you already farmed a Meteorite crash site for Meteorite, you can use the excellent with : its piercing ability will clear out the Creepers fairly easily, and it will cost no mana thanks to the set bonus of Meteor armor. As of, meteorites now only spawn after the Brain of Cthulhu has been defeated. However, this is still a valid strategy if you have already defeated the Brain of Cthulhu at least once.

For Throwing users:
 * Non-explosive consumables, such as and, can be effective since they penetrate multiple enemies, meaning that they can hit multiple Creepers.
 * with their Penetration are very helpful for killing Creepers. Since they take a while to disappear, it's a good idea to throw many of them into your arena before starting the fight.
 * If you are willing to risk, are great choices for dealing with the Creepers, but you have to watch out for the blast radius, as you will take damage from it.
 * , while expensive to make (as aren't common), is a superb weapon. The splash damage and the fire that hits multiple times can keep the Brain away in its second stage.

For Summoners:

At this stage of the game, it's better to use any of the already mentioned Gear tips, as there isn't much to use, unless you want to kill first, which is not recommended at this time.

Potions

 * The, the and the  will do you well.
 * You should try to get the Buff in some way; you can get this from  or (except on ).
 * On the, you could do even better with the buff, which is easily obtainable from , , or similar.
 * Better yet is the buff (which is most easily obtained from  or else from the rare  drop, the ).

Accessories

 * The will give you a double-jump ability which will greatly help with evasion. Look out for the alternative versions, some of which are more performant: the, the , the , or the.
 * The will increase your speed and aid greatly in evasion. You can upgrade them to the  for the added bonus of a few seconds of flight, but this requires the, which the player may not have yet.
 * The 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 gives a basic 10% speed boost, which will help out with evasion. You can replace it with the  which is much easier to find but only offers a 5% speed boost.
 * The will give you improved jumping abilities, including increased height and automatic jumping but it can only be found by fishing, though it is rather rare.
 * If one is playing in Expert mode, the is a great choice for quick evasion, and extra damage in the Brain's second phase.

fr:Guide:Stratégies du Cerveau de Cthulhu