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Brain of CthulhuFirst Form
Brain of Cthulhu (First Phase)
Map Icon Brain of Cthulhu
Map Icon
Classic mode icon Classic
Expert mode icon Expert
Master mode icon Master
AI TypeBrain of Cthulhu AI
Max Life1250/2125/2709
325055257029 (with creepers) [1]
KB Resist100%
Immune toConfused
Brain of CthulhuSecond Form
Brain of Cthulhu (Second Phase)
Map Icon Brain of Cthulhu
Map Icon
Classic mode icon Classic
Expert mode icon Expert
Master mode icon Master
AI TypeBrain of Cthulhu AI
Max Life1250/2125/2709
KB Resist55%60%65%
Immune toConfused
Brain of Cthulhu Trophy"A horrible chill goes down your spine..."Brain of Cthulhu Trophy
For the Old-gen console version Old-gen console, Windows Phone version Windows Phone, and 3DSNintendo 3DS version pet summon, see Brain.

The Brain of Cthulhu is a pre-Hardmode, Crimson-themed boss resembling a large, flying brain. It can be summoned when 3 Crimson Hearts are destroyed in a Crimson world, or when a player uses a Bloody Spine anywhere in The 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 of Cthulhu is the Crimson counterpart to the Eater of Worlds. Unlike its Corruption counterpart, it does not have a mechanical equivalent in Hardmode.

While the Brain of Cthulhu is alive, the music Boss 3 will play. When Otherworldly music is enabled, the track Boss 1 (Otherworldly) will play instead.


First phase[]

The Brain itself is initially invincible. It teleports around the player, drawing nearer before teleporting away again in a random direction while its CreeperCreeper 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.

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.

Expert Mode[]

  • In Expert mode, the Brain of Cthulhu gains a 70% health increase. This brings its original Classic Mode health of 1250 health up to 2125 health.
    • The Creepers gain a health increase of the same percentage, going from 100 health up to 170 health. This brings the boss's overall health up from 3250 health to 5525 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 bossfight goes on with time.
  • 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.[2]
Debuff Duration [2] Chance (Brain) Chance (Creepers)
Expert Mode Master Mode
PoisonedPoisoned 5.25 - 10.5 seconds 6.56 - 13.13 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%)
DarknessDarkness 3 - 6 seconds 3.75 - 7.5 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%)
CursedCursed 0.75 - 1.5 seconds 0.94 - 1.88 seconds 0.82*2/243 (0.82%) 2.47*2/81 (2.47%)
BleedingBleeding 7.5 - 15 seconds 9.38 - 18.75 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%)
ConfusedConfused 1.5 - 3 seconds 1.88 - 3.75 seconds 0.82*2/243 (0.82%) 2.47*2/81 (2.47%)
SlowSlow 5.25 - 10.5 seconds 6.56 - 13.13 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%)
WeakWeak 11.25 - 22.5 seconds 14.06 - 28.13 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%)
SilencedSilenced 1.5 - 3 seconds 1.88 - 3.75 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%)
Broken ArmorBroken Armor 9.75 - 19.5 seconds 12.19 - 24.38 seconds 4.53*11/243 (4.53%) 13.58*11/81 (13.58%)

Master Mode[]

  • All Expert mode changes apply.
  • In Master Mode, the Brain of Cthulhu gains a 27.48% health increase. This brings its original Expert Mode health of 2125 health up to 2709 health.
    • The Creepers gain a health increase of the same percentage, going from 170 health up to 216 health. This brings the boss's overall health up from 5525 health to 7029 health.
  • The debuffs inflicted by the Brain and the Creepers are extended in duration, as detailed in the table above.
  • (Tested in a pre-hardmode For The Worthy world) In its second phase, Brain of Cthulhu will also flip gravity, which will prevent gravitation potions from working. The gravity effect prevents the player from standing on platforms, so be mindful of this when building your arena.

Health in Multiplayer[]

  • In Expert and Master modes, the health of bosses depends on the number of players in multiplayer. Please enter the number of players (a whole number between 2 and 256) on your server in the input box below.

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  • Brain of Cthulhu


    • Creepers drop Hearts at a higher rate than most enemies.
    • Creepers are more aggressive in Expert Mode and Master Mode.
    • If all players die, or leaves the Crimson, the Brain of Cthulhu will move downwards and despawn.
      • However, if players return to the Crimson before the Brain of Cthulhu despawns, the battle will continue as normal.
    • 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.
      • However, defeating the Brain of Cthulhu is the only way to gain access to the Tavernkeep and, as of , Meteorites.
    • 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.


    Achievement Mastermind
    Mastermind • Defeat the Brain of Cthulhu, an enormous demon brain which haunts the creeping crimson.
    Defeat the Brain of Cthulhu for the first time.
    Category: Slayer Slayer


    For more elaborate strategies on defeating Brain of Cthulhu, including weapon and arena recommendations, see Guide:Brain of Cthulhu strategies.
    • 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.
    • In the case you've acquired one, the Demon Scythe is an exceptional weapon against both of the brain's phases (particularly the first) thanks to its high damage, pierce and knockback.
    • 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.
    • In the early game of Expert Mode or Master Mode, it may be advantageous to block off most entrances to the place you are fighting Brain of Cthulhu to prevent crimson Enemies from spawning and interrupting the first phase of the fight.
      • Bringing along a Summon weapon can also be useful in deterring crimson Enemies if they do not target the Creepers.
    • When fighting the Brain of Cthulhu on higher difficulties, it may be wise to only apply buffs once you have safely exited the tunnel used to smash the Crimson Heart, since the brain may block your path, killing you in seconds. It could be preferable to use Dynamite to destroy the last heart over a hammer or bombs, due to its longer explosion delay.
    • There are several methods to reveal the real Brain of Cthulhu in the second stage:
      • A Hunter Potion will only highlight the real Brain.
      • 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.
      • 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.
    • If you're able to keep the Creepers at bay, try watching the minimap during the first phase. It can communicate where the brain's new position after teleporting is before your eyes can register it on-screen, giving you time to avoid accidentally running directly into it.


    Brain of Cthulhu cloud

    The Brain of Cthulhu-shaped cloud.

    • 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.
      • Official Terraria Lore – 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 Brain of Cthulhu 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 PC version PC version, Console version Console version, Mobile version Mobile version, and tModLoader version tModLoader version, a cloud in the shape of the Brain of Cthulhu can occasionally be seen in the background.
    • According to the lore, the Dryads ripped out only a few chunks of Cthulhu’s brain, so it may not be the whole brain.

    The BestiaryBestiary 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 Fixed Brain of Cthulhu teleporting too close to the player in For the worthy/Everything Seed Seeds. It should no longer be able to directly telefrag the player, but the Brain is not avoiding you, so a rapidly moving player may still find themselves in its new teleport position.
    • Desktop Fixed a grammatical error in the Bestiary description: "... aids the Crimson to an attempt to avenge ..." to "... aids the Crimson in an attempt to avenge ...".
    • Desktop 1.4.4:
      • Health increased from 1000 to 1250
      • 5% Knockback resistance added across all difficulties (50/55/60% to 55/60/65%)
      • Expert/Master illusions now become opaque much faster
      • There is now a safe range around the player during Phase 1 to prevent BoC from teleporting directly on top of you (though it can still be extremely close)
      • No longer has a map icon during Phase 2
    • Desktop 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 1.2.3:
      • Killing the Brain of Cthulhu will now allow the Dryad to move into your town.
      • Now has a chance to drop the Brain Mask.
      • Fixed bug where beating Brain of Cthulhu wouldn't make dryad stop talking about the chasms.


    1. Information taken from the PC version PC source code, method AI() in Terraria.NPC.cs (under aiStyle == 54); also method GetBrainOfCthuluCreepersCount() in Terraria.NPC.cs There may be inaccuracies, as the current PC version PC version is
    2. 2.0 2.1 Information taken from the PC version PC source code, methods StatusFromNPC() and AddBuff_DetermineBuffTimeToAdd() in Terraria.Player.cs There may be inaccuracies, as the current PC version PC version is