|AI Type||Brain of Cthulhu AI|
- Internal NPC ID: 266
The Brain of Cthulhu is a pre-Hardmode Crimson-themed boss resembling a large, flying brain. It can be summoned when players destroy 3 Crimson Hearts in a Crimson world, or when a player uses a Bloody Spine anywhere in a Crimson or Underground Crimson biome.
The Brain of Cthulhu has two stages. In the first, the Brain is invulnerable and teleports randomly around the player. 20 Creepers spawn along with the Brain and orbit the boss at high speed. Creepers do not respawn once they are killed. All Creepers must be destroyed first before the Brain of Cthulhu enters its second phase, where it becomes vulnerable to attack and can be killed.
Defeating the Brain of Cthulhu and its attendant Creepers is the only way to obtain Tissue Samples, and is one of the ways to obtain usable quantities of Crimtane Ore. Defeating the Brain of Cthulhu for the first time allows the Tavernkeep NPC to spawn.
The Brain itself is initially invincible. It teleports around the player, drawing nearer before teleporting away again in a random direction while its Creeper minions attack the player. The Creepers do not teleport along with the Brain but are instead pulled between the player and the Brain in large, sweeping orbits, forming groups and allowing the player to deal damage to all the Creepers at the same time. Once all Creepers are defeated, the Brain enters its second phase.
In the second phase, the Brain becomes vulnerable to attacks and knockback and it aggressively attempts to ram the player while rapidly teleporting around.
- In Expert mode, the Brain of Cthulhu gains a 70% health increase. This brings its original Classic Mode health of 1000 health up to 1700 health.
- In Expert mode, the second phase now has three mirror images of the Brain appear around the player, mirroring the Brain's movements and becoming more opaque as the boss loses health.
- Furthermore, both the Creepers (in the first phase) and the Brain (in the second phase) inflict a random debuff upon contact. The probabilities of applying each debuff are listed in the following table; note that the Creepers always inflict a debuff while the Brain only has a
33.33*1/3 (33.33%) chance to do so. Debuff Duration  Chance (Brain) Chance (Creepers) Expert Mode Master Mode Poisoned 5.25 - 10.5 seconds 6.56 - 13.13 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%) Darkness 3 - 6 seconds 3.75 - 7.5 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%) Cursed 0.75 - 1.5 seconds 0.94 - 1.88 seconds 0.82*2/243 (0.82%) 2.47*2/81 (2.47%) Bleeding 7.5 - 15 seconds 9.38 - 18.75 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%) Confused 1.5 - 3 seconds 1.88 - 3.75 seconds 0.82*2/243 (0.82%) 2.47*2/81 (2.47%) Slow 5.25 - 10.5 seconds 6.56 - 13.13 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%) Weak 11.25 - 22.5 seconds 14.06 - 28.13 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%) Silenced 1.5 - 3 seconds 1.88 - 3.75 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%) Broken Armor 9.75 - 19.5 seconds 12.19 - 24.38 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%)
- All Expert mode changes apply.
- In Master Mode, the Brain of Cthulhu gains a 27.47% health increase. This brings its original Expert Mode health of 1700 health up to 2167 health.
- The debuffs inflicted by the Brain and the Creepers are extended in duration, as detailed in the table above.
- Creepers drop Hearts at a higher rate than most enemies.
- Creepers are more aggressive in Expert Mode and Master Mode.
- If the player leaves the Crimson, the Brain of Cthulhu will despawn.
- Two Brains can be summoned at once by smashing Crimson Hearts. They seem to share their Creepers and go into their second phases simultaneously.
- Note that actually defeating the Brain of Cthulhu is not completely necessary to progress, as the Creepers may drop the needed amount of materials.
- Crafting the Deathbringer Pickaxe (from Tissue Samples and Crimtane Ore) will not be necessary if the player obtains the Reaver Shark (through fishing).
- Since Hellstone can be destroyed with explosives in Hardmode, and Hardmode ores can be obtained from fishing, defeating the Brain of Cthulhu is not necessary to obtaining those items.
- Creepers have low individual health and are especially susceptible to the On Fire! and Frostburn debuffs. Weapons that inflict these debuffs can make quick work of them.
- Grenades and other splash damage weapons can kill the Creepers very quickly, as they will bunch up often.
- Since the Brain of Cthulhu is susceptible to knockback, weapons with high knockback such as the The Rotted Fork can keep both Creepers and the Brain from closing distance between teleports. It is also possible to use early-game melee weapons such as the Katana or the Zombie Arm as long as they do not have disadvantageous modifiers. It is preferable to use spears for this fight since they deal more knockback, however, so the Trident or The Rotted Fork is recommended.
- Note that this may not work in Expert Mode, since it might be hard to tell which Brain to attack among the illusions.
- Jester's Arrows or other enemy-piercing weapons can be immensely helpful while fighting the first stage, since Creepers often group up in a clustered formation, effectively allowing the player to hit most if not all of the Creepers in one well-aimed shot.
- The Minishark is extremely effective in keeping the Brain of Cthulhu away from the player during the second stage.
- The Quad-Barrel Shotgun is an excellent weapon to use for the brain's second form. It deals extremely high close-range damage and can end the fight before the Brain’s illusions get too opaque.
- There are several methods to reveal the real Brain of Cthulhu in the second stage:
- A Hunter Potion will only highlight the real Brain.
- On the For The Worthy seed fake Brains are also highlighted.
- The real Brain is the only one with a health bar.
- Bone Javelins only stick out of the real Brain.
- The On Fire! and Poisoned debuffs damage only the real Brain.
- The Slime Gun and Water Gun cause visual effects only to the real Brain. Note that these do not deal damage.
- The Slime Mount only bounces off the real Brain.
- The illusions position themselves in relation to the player. The illusions will quickly spread away from the real Brain if the player is walking away from it, but the real Brain will continue to move at a steady pace.
- The minimap displays only the real Brain.
- When using a controller, the lock on feature will only target the real Brain.
- Selling all the Crimtane Ore that can be obtained from the fight is a very effective way to make money in pre-Hardmode.
- The Brain of Cthulhu, among several other bosses, is based on Cthulhu, a creature first imagined by H. P. Lovecraft in his short story The Call of Cthulhu.
- Unlike the correlation between the Eater of Worlds and The Destroyer, the Brain of Cthulhu does not have a Hardmode counterpart, although The Destroyer's Probes are similar in function to its Creepers.
- – According to the official game lore, the Mechanic never finished Cthulhu's mechanical brain, thus explaining its lack of a mechanical counterpart.
- On a technical level, the reason the BoC has no mechanical version is because the mechanical bosses were introduced in desktop 1.1, whereas the BoC was introduced in desktop 1.2
- The Brain of Cthulhu has the least health out of all the bosses, with even less than the Eye of Cthulhu in its second form. However, when adding in the health of the Creepers, it has more health than King Slime.
- The Brain is the only boss that is affected by knockback.
- Contrary to popular belief, Creepers do not drop Souls of Night, Biome Keys, or Biome Key Molds.
- It is one of the only three bosses whose map icon does not change after entering its second phase, the others being Santa-NK1, and Queen Slime.
- The Brain of Cthulhu is sometimes abbreviated as "BoC."
- The list of debuffs inflicted by the Brain and Creepers in Expert Mode just so happens to be exactly the same as the list of debuff immunities granted by the Ankh Charm. The Ankh Shield also gives these immunities, with the addition of Burning and Chilled. Of course, it is fairly trivial to defeat the Brain of Cthulhu at the point in the game that the Ankh Charm can be obtained.
- On the Desktop version, Console version, and Mobile version, a cloud in the shape of the Brain of Cthulhu can occasionally be seen in the background.
- The Bestiary entry for the Brain of Cthulhu: "A piece of Cthulhu torn asunder, this vile mastermind pulses with agony and aids the Crimson in an attempt to avenge its master."
- Desktop 220.127.116.11: Sprite updated.
- Desktop 18.104.22.168: Defeating the Brain of Cthulhu now allows Meteorites to fall rather than breaking a Crimson Heart, and defeating more Brains of Cthulhu will increase the chance of a Meteorite falling the following night.
- Desktop 22.214.171.124:
- Desktop 1.2.3:
- Desktop 1.2: Introduced.
- Console 1.02: Introduced.
- Switch 1.0.711.6: Introduced.
- Mobile 1.2.6508: Introduced.
- 3DS-Release: Introduced.
- Information taken from the Desktop 126.96.36.199 source code, method
); also method
aiStyle == 54
There may be inaccuracies, as the current Desktop version is 188.8.131.52.
- Information taken from the Desktop 184.108.40.206 source code, methods
There may be inaccuracies, as the current Desktop version is 220.127.116.11.