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Boss Delirium name.png
Boss versus screen image
Table dividing line 1.png
In-game appearance
Table dividing line 2.png
Stage the void.png
Table dividing line 3.png
Final Boss Chest
Added in Afterbirth †

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 instances of the same boss.
    • Whether it turns into champion variants or regular variants is random and does not depend on which variant was previously defeated. For instance, it can turn into black Gurdy, even if the regular Gurdy was the defeated variant, and vice-versa.
    • 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 burst into blood and drop a Final Boss Chest, playing the Final Ending.


Unlockable Achievements


  • Delirium's boss music is named after Delirium itself.
  • 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 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 and Ultra Greed) 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.
    • The Gurglings originally lacked unique Delirium sprites, though this was later patched in a Booster Pack.
  • When transformed into a boss that has multiple segments, the extra segments can be killed. The head, however, cannot.
    • This also applies to Gemini - Suture can be killed but Contusion 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.
  • When transformed into two instances of the same boss, one of them can be killed but the other cannot.
  • When transformed into the Gurglings or the Turdlings, it will only appear as one instead of two.
  • When transformed into The Headless Horseman, it transforms into either the head or the body, but it doesn't transform into both.
  • The sizes of Fistula and Teratoma depend entirely on chance.
  • There was a glitch in the original version of The Binding of Isaac: Afterbirth † which caused Delirium's main form to lack an idle animation. This was soon patched.
  • In the game files, there is an unused Delirium transformation of Ultra Greed with a beard.
  • Unlike the real Mom, Delirium's Mom form will only stomp and will not spawn enemies.
  • 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.
    • Another word with a similar meaning to delirium is “dementia”.
  • 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.
  • Every time Delirium transforms into another boss, it adds onto the encounters counter in the Bestiary.
  • If Delirium transforms into Gemini then undergoes another transformation, Suture doesn't disappear. Instead, he will come after the player like the normal version does after Contusion is killed.
  • If Delirium transforms into The Lamb's second phase then undergoes another transformation, the body doesn't disappear and can be killed, just like the real Lamb's body.
  • Prior to Booster Pack #5, Delirium could transform into a Lil' Haunt.


Bug Bug! 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.
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, 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! 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
Stage basement.png
Stage cellar.png
Stage burning basement.png
Blighted OvumDingleThe Duke of FliesFamineFistulaGeminiGurglingsThe HauntLarry Jr.MonstroPinStevenWidow
Added in Afterbirth DangleLittle HornRag ManTurdlings
Chapter 2
Stage caves.png
Stage catacombs.png
Stage flooded caves.png
Carrion QueenC.H.A.D.ChubDark OneGurdyGurdy Jr.The HollowThe HuskMega FattyMega MawPeepPestilencePolycephalusThe Wretched
Added in Afterbirth The ForsakenThe FrailThe Stain
Added in Afterbirth † Big HornRag Mega
Chapter 3
Stage depths.png
Stage necropolis.png
Stage dank depths.png
The AdversaryThe BloatThe CageThe GateGishLokiMask Of InfamyMonstro IIWarMom
Added in Afterbirth Brownie
Added in Afterbirth † Sisters Vis
Chapter 4
Stage womb.png
Stage utero.png
Stage scarred womb.png
BlastocystThe BloatConquestDaddy Long LegsDeathLokiiMama GurdyMr. FredScolexTeratomaTriachnidMom's HeartIt Lives
Added in Afterbirth † Sisters VisThe Matriarch
Added in Afterbirth Blue Womb
Added in Afterbirth Hush
Chapter 5
Stage sheol.png
Stage cathedral.png
Chapter 6
Stage dark room.png
Stage chest.png
???The LambMega Satan
Added in Afterbirth Greed Mode
Ultra Greed
Added in Afterbirth Ultra Greed
Added in Afterbirth † Ultra Greedier
Added in Afterbirth † The Void
Stage the void.png
Added in Afterbirth † Delirium
Chapters 1-4 The FallenThe Headless Horseman

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