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Added in Afterbirth †
Boss Delirium.png
Base HP
Stage HP
Found In
Stage the void.png
Dropped Items
Final Boss Chest

Delirium is a boss added in the expansion The Binding of Isaac: Afterbirth †. It is the final boss of The Void, and is the final boss of the series as a whole.


  • Delirium will teleport around the room, sending out an array of white projectiles and green projectiles that explode like Ipecac.
  • Its most notable (and dangerous) attack is that it will transform into bosses previously encountered during the run, including a few of the "final" bosses (Mom, It Lives, etc.).
    • While transformed, it will attack with its white projectiles along with the attacks of the boss it is transformed into, though it cannot attack with its explosive projectiles.
    • When it transforms into a boss, Delirium retains its own health, not the health of the boss it transformed into.
    • The attacks of the transformed boss are dependent on Delirium's current HP. For example, if Delirium transforms into War while at <50% HP, it will be horseless and run at Isaac.
    • It can rarely transform into two or three instances of the same boss.
    • It is unable to properly transform into Hush.
  • Progressively, it will alternate through each form faster and become more aggressive.

Upon defeat, the screen will start to glitch and fill with static while short moments from the current run are played. After being defeated, Delirium will drop a Final Boss Chest, playing the Final Ending.

Unlockable Achievements

Nintendo Switch exclusive


  • Delirium's boss music is named after Delirium itself.
  • On Isaac's last will, Delirium will be shown in its current form rather than its main one. Sometimes it will show his main form, even if Isaac is killed by a different form.
  • Delirium is the only enemy immune to Chaos Card.
    • When it changes into an enemy like Chub with multiple hitboxes, if one of the secondary hitboxes is hit by Chaos Card, it will kill Delirium in one hit. However, this can crash the game, so it's best to simply not use the Chaos Card during the battle.
  • As a single stage boss, Delirium can be instantly killed by Plan C, but Isaac will still be killed first by its effects, as Delirium's death animation is longer than 3 seconds.
  • Killing Delirium in a daily run counts as winning it.
  • Unlike other completion marks, defeating Delirium does not add a mark to the post-it note. Instead, the note will become tattered (with blood on hard mode).
  • If no other bosses have been fought, Delirium will be unable to transform.
  • Delirium can turn into a Lil' Haunt, which is the only enemy it can turn into that is not a boss.
  • Delirium can transform into bosses featured in custom mods, though it will not have unique sprites by default.[1] This is probably because Delirium takes other bosses' A.I. and uses them in sync with his own sprites, if he has the appropriate boss sprites.
  • Delirium can transform into mini-bosses such as the seven deadly sins, but they don't have Delirium skins. [citation needed]
  • Delirium can transform into either form of Satan.
  • Delirium can turn into Hush's second form if it's the only boss encountered in the run or very few bosses have been encountered in the run; this can be done with the debug console, [citation needed] though this is technically a bug, as the sprite is unfinished and many of the attacks don't work properly.
    • It can also transform into Hush if the form has been encountered by spawning it in with Delirious.
  • Every boss in the game (with the exception of the fallen angels) has Delirium versions complete with their sprites and animations, including the unfinished Delirium version of Hush.
    • If it transforms into Fallen Uriel or Fallen Gabriel, it will use their Fallen skins, not their Delirium skin.
    • If it transforms into Mega Satan, the Sprite will bug out. It can attack normally, but the sprite may not be visible/half visible/only showing the hands.
  • When transformed into a boss that has multiple segments, the extra segments can be killed. The head, however, cannot.
    • This also applies to Gemini - Contusion can be killed but Suture cannot.
    • All parts of Fistula and Teratoma can be killed (though they have much greater health than normal), and the room will remain empty until Delirium transforms again. Even though the segments have been killed, Delirium itself has not been killed.
  • The sizes of Fistula and Teratoma depend entirely on chance.
  • In the game files, there is an unused Delirium transformation of Ultra Greed with a beard.
  • Delirium's form of It Lives has it's eyes open, as opposed to the original's closed ones.
  • The word "delirium" means "madness" or "derangement". A delirium is a state of mind characterized by disorganized behavior, incoherence, hallucinations, and delusions. Delirium is meant to represent Isaac's current state of mind; he is experiencing his own delirium, and the battle is meant to represent his battle against his own madness.
  • Delirium is Isaac's manifestation of the "white light at the end of the tunnel" where the entire history of his life flashes before his eyes, moments before Isaac's death[2]
    • This might be reflected by Delirium's death animation and its ability to shapeshift into different bosses you previously encounter.


Bug Bug! Delirium can sometimes deal unavoidable glitched damage. For example, when transformed into Mom, Isaac can sometimes take damage before Mom's leg actually stomps.
Bug Bug! Sometimes, when Delirium transforms into a segmented boss or a Lil' Haunt, its health will appear to be lower than it actually is. This is usually purely visual and returns to normal whenever it transforms again, though it is possible that it will not return to normal.[3]
Bug Bug! Delirium has been observed to turn into Dank Squirts if it transforms into a Black Champion Brownie at low health. Killing them will be considered killing Delirium and the endgame chest will appear.[4]
Bug Bug! Enabling "debug 10" using the Debug Console (which makes every enemy take constant damage) will cause Delirium to die and continually fill the screen with static until the command is disabled.



Bosses Boss Monstro.png
Chapter 1 Blighted OvumDingleThe Duke of FliesFamineFistulaGeminiGurdy Jr.GurglingsThe HauntLarry Jr.MonstroPinStevenWidow
Added in Afterbirth DangleLittle HornRag ManTurdlings
Chapter 2 C.H.A.D.ChubDark OneGurdyGurdy Jr.The HollowThe HuskMega FattyMega MawPeepPestilencePolycephalusCarrion QueenThe Wretched
Added in Afterbirth The ForsakenThe FrailThe Stain
Added in Afterbirth † Big HornRag Mega
Chapter 3 The AdversaryThe BloatThe CageCarrion QueenThe GateGishLokiMask of InfamyMonstro IIWarThe WretchedMom
Added in Afterbirth Brownie
Added in Afterbirth † Sisters Vis
Chapter 4 BlastocystThe BloatConquestDaddy Long LegsDeathIt LivesLokiiMama GurdyMom's HeartMr. FredScolexTeratomaTriachnid
Added in Afterbirth Blue Womb Added in Afterbirth Hush
Chapter 5 The FallenIsaacSatan
Chapter 6 ???The LambMega Satan
Added in Afterbirth Greed Mode Added in Afterbirth Ultra Greed
Added in Afterbirth † Ultra Greedier
Added in Afterbirth † The Void Added in Afterbirth † Delirium
Chapters 1-4 The FallenThe Headless Horseman

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