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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 icon.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 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.


  • Delirium is immune to Chaos Card.
  • Plan C is ineffective against Delirium. Because his death animation is longer than 3 seconds, Isaac will still be killed first.
  • Most entities that are considered to be bosses by the game (usually identified by ones that add the boss health bar to the screen) are marked as bosses that Delirium can transform into.
    • The Seven Sins are exceptions to this.
    • Delirium can transform into either form of Satan.
    • 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.
    • Each size of Fistula and Teratoma count as their separate boss which Delirium can transform into just like any other boss.
    • This also results in many bugs due to unaccounted for transformations. These can be viewed in the Bugs section of this page.
    • 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 (like Lokii or Sisters Vis), one of them can be killed but the other cannot.
  • Unlike the real Mom, Delirium's Mom form will only stomp and will not spawn enemies.
  • 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.


Unlockable Achievements


  • Delirium is the only enemy immune to Chaos Card.
  • Killing Delirium in a daily run counts as winning it. However, this does not reward any unique bonus points.
  • 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 encountered during the run, Delirium will be unable to transform.
    • This is normally impossible as you have to defeat at least one boss, even if extremely lucky. Use floor skips such as Ehwaz or We Need to Go Deeper! until Chapter 3. After the fight with Mom, Isaac has a 5% chance of teleporting to The Void, but only if Isaac has 10+ tear damage or 20+ items. Then, you must find Delirium without encountering any other bosses.
  • 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.
    • Delirium can transform into Ultra Greed if he is encountered, but this is normally impossible as the bosses never appear in the same game mode.
  • 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.[1]
    • 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.
  • Delirium as Steven resembles Ash from The End is Nigh.


Bug Bug! If Delirium transforms into an enemy like Chub with multiple hitboxes, the game may crash if one of the secondary hitboxes is hit by Chaos Card.
Bug Bug! Delirium can transform into Hush if very few bosses have been encountered during that run, but the sprites are unfinished and many of the attacks do not work properly.
Bug Bug! Delirium can transform into Fallen Uriel and Fallen Gabriel, but they do not have unique Delirium skins.
Bug Bug! If Delirium transforms into Mega Satan, the sprites will bug out. It can attack normally, but the sprite may not be visible/half-visible/only showing the hands.
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 unavoidably glitched damage. For example, when transformed into Mom, Isaac can sometimes take damage before Mom's leg stomps.
Bug Bug! Sometimes, when Delirium transforms into a segmented boss, its health will appear to be lower than it is. This is usually purely visual and returns to normal whenever it transforms again, though it may not return to normal.[2]


Bosses Boss Monstro.png
Chapter 1
Stage The Basement icon.pngStage The Cellar icon.pngStage Burning Basement icon.png
Blighted OvumDingleThe Duke of FliesFamineFistulaGeminiGurglingsThe HauntLarry Jr.MonstroPinStevenWidowThe FallenThe Headless Horseman
DangleLittle HornRag ManTurdlings
Chapter 2
Stage The Caves icon.pngStage The Catacombs icon.pngStage Flooded Caves icon.png
Carrion QueenC.H.A.D.ChubDark OneGurdyGurdy Jr.The HollowThe HuskMega FattyMega MawPeepPestilencePolycephalusThe WretchedThe FallenThe Headless Horseman
The ForsakenThe FrailThe Stain
Big HornRag Mega
Chapter 3
Stage The Depths icon.pngStage Necropolis icon.pngStage Dank Depths icon.png
The AdversaryThe BloatThe CageThe GateGishLokiMask Of InfamyMonstro IIWarThe FallenThe Headless HorsemanMom
Sisters Vis
Chapter 4
Stage The Womb icon.pngStage Utero icon.pngStage Scarred Womb icon.png
BlastocystThe BloatConquestDaddy Long LegsDeathLokiiMama GurdyMr. FredScolexTeratomaTriachnidThe FallenThe Headless HorsemanMom's HeartIt Lives
Sisters VisThe Matriarch
Blue Womb
Chapter 5
Stage Sheol icon.pngStage Cathedral icon.png
Chapter 6
Stage Dark Room icon.pngStage The Chest icon.png
???The LambMega Satan
The Void
Stage The Void icon.png
Greed Mode
Ultra Greed
Ultra Greed
Ultra Greedier
The Binding of Isaac: Rebirth The Binding of Isaac: Rebirth The Binding of Isaac: Rebirth
Achievements Achievements Attributes Attributes Bosses Bosses TarotCard.png Cards and Runes Challenges Challenges Chapters Chapters
Characters Characters MainPageBabies.png Co-op Items Items Item pools Item pools Monsters Monsters Objects Objects
Pickups Pickups Pills Pills Rooms Rooms Seeds Seeds Transformations Transformations Trinkets Trinkets