Binding of Isaac: Rebirth Wiki
Binding of Isaac: Rebirth Wiki

Added in Afterbirth †

Delirium is a boss added in The Binding of Isaac: Afterbirth †. It is the main boss of The Void The Void and the final boss of Ending 20.


Delirium's main form is stationary but teleports erratically around the room and performs the following attacks:

  • Continuously sends out various overlapping patterns of white projectiles for the entire duration of the fight:
    • 20 projectiles that slowly rotate clockwise or counterclockwise slowly while expanding.
    • 16 projectiles outwards in all directions.
    • 14 projectiles that rotate clockwise, counterclockwise, or back and forth while expanding.
    • 10 projectiles that fluctuate in and out while expanding.
    • 8 slow-moving green-tinted 15►Ipecac Ipecac projectiles in all directions.
    • 6 projectiles that travel outwards in a zig-zag pattern.
    • 4 projectiles outwards in a lop-sided cross.
    • 4 lines of 3 projectiles that spiral outwards.
    • A spread of 5 projectiles in Isaac's direction.
    • A burst of projectiles that travel outwards in random directions.
    • A stray short-range projectile in a random direction.
      • The projectile size per each attack is random and varies from very small to moderately large.
  • Transforms into bosses previously encountered during the run, which can include major bosses such as Mom or It Lives.
    • When it transforms into a boss, Delirium retains its own health, not the health of the boss it transformed into.
    • When transforming into certain multi-phase bosses such as Isaac, Delirium copies the phase that that boss would be at, given its current health percentage.
    • It can rarely transform into two bosses at once.
    • Whether it turns into a Champion variant or a regular variant is random and does not depend on which variant was previously defeated.
    • Removed in Repentance It is unable to properly transform into Hush's true form. In order for this to happen, very few bosses must be encountered in the run. Additionally, many of Hush's attacks do not work properly and the sprite is also unfinished.
    • Added in Repentance Can transform into Baby Plum, Bumbino, Reap Creep, and The Pile, but only Baby Plum has a unique sprite. Cannot transform into any other Repentance bosses.
  • Occasionally, it returns to its main form to perform projectile attacks at a faster pace.
  • As it takes damage it becomes more aggressive: moving, teleporting, transforming, and attacking at a faster rate.
    • It also takes on reddish hue to signify this change.

Upon defeat, the screen starts to glitch, fills with static, and the room switches between different environments, while short scenes from the current run are played ending with Delirium screaming and bursting into a small puddle of blood.


Unlockable Achievements[]

Damage Scaling[]

Damage scaling is an unclear mechanic introduced by Nicalis in The Binding of Isaac: Afterbirth to provide a more challenging experience to the players, enabling some enemies to retaliate against high damage attacks by deploying an "armor" of a sort to greatly reduce the amount of damage taken. Further details and an in-depth explanation may be found here.

Delirium only has damage scaling while transformed, not while in its main form.


  • Delirium is immune to Chaos Card Chaos Card.
  • 15►Plan C Plan C is ineffective against Delirium. While it does kill Delirium, because its death animation is longer than 3 seconds, Isaac will still be killed first.
    • It works with 15►Lazarus' Rags Lazarus' Rags as it revives Isaac on the spot. However, the Completion Mark will go toward Lazarus, not the character originally selected.
    • Added in RepentanceSoul of Lazarus Soul of Lazarus and Added in Repentance15►Inner Child Inner Child revive Isaac in the same room he died in, and the Completion Mark goes toward the selected character.
    • While playing as Tainted Lost Tainted Lost, Added in Repentance15►Birthright Birthright revives him inside Delirium's room without transforming himself into another character.
  • 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, since they are somehow considered as mini-bosses.
    • Although Grubs can spawn in Larry Jr. boss fights, they are still not considered as bosses (and do not have the boss health bar), so Delirium cannot transform into a Grub.
    • Delirium can transform into either form of Satan.
    • When transformed into the Gurglings or the Turdlings, it only appears 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.
    • All parts of Fistula and Teratoma can be killed (though they have much greater health than normal), and the room remains 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 (until Delirium's hp fully runs out).
    • If Delirium transforms into Pink Champion Monstro, it only takes the form of one and summons an extra Pink Champion Monstro.
    • 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 original Lamb's body.
      • Killing this body will cause the screen to become darker for a period of time, just like when you kill the original Lamb's body.
      • Delirium can also transform into the Lamb's body on its own. If this happens, the body disappears when Delirium transforms again.
  • 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.
      • If Delirium transforms into Gemini then undergoes another transformation, Suture doesn't disappear. Instead, he continues to chase Isaac as if Contusion was killed in the original fight.
  • Delirium's Mom form only stomps and does not spawn enemies.


  • 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 is reflected by Delirium's death animation and its ability to shapeshift into previously encountered bosses.
  • "Delirium" is the state of mental confusion of a person who is delirious. Symptoms include restlessness, illusions and incoherence.
  • The arena can randomly change themes during the fight and is purely visual.
  • Delirium is one of only two enemies immune to Chaos Card Chaos Card, the other being Added in Repentance The Beast.
  • Killing Delirium in a daily challenge 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 is unable to transform.
  • 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.
  • Every time Delirium transforms into another boss, it adds onto the encounters counter in the Bestiary.
  • If Delirium transforms into Mom as soon as the battle starts, it stomps in the center of the room regardless of Isaac's position, similar to how the original Mom always starts her battle by stomping in the center of the room.
    • Similarly, If Delirium transforms into Mom's Heart/It Lives as soon as the battle starts, it is accompanied by two Eyes in the same position as they are when they accompany the original Mom's Heart/It Lives at the start of its battle.
  • Prior to Booster Pack #5, Delirium could turn into a Lil' Haunt.
    • Also, if it transformed into Black Champion Brownie when at low health, It would spawn two Dank Squirts like the original boss would and die before the health bar actually fully depleted, without playing its death animation. This no longer happens because Delirium's Brownie form (normal and Black Champion) no longer transitions into the second phase (turning into a weakened Dangle or leaving two Dank Squirts, respectively).
  • Delirium uses the exact same sprite for both its Dingle and Dangle forms.
  • Added in Repentance Delirium’s sprite for its Steven form is based on Ash from The End Is Nigh.
  • If Delirium transforms into Mega Fatty and performs the vomit attack, it attracts its White and Green projectiles towards it.
  • The 15►Crack the Sky Crack the Sky beam attack summoned by Delirium as Isaac only covers around 1/3rd of the room starting from a corner.
  • The only bosses Delirium can't normally transform are Ultra Greed, Ultra Greedier, Hush (it can, but via cheats or bugs) and any other Repentance boss except for those that can appear on the "main" route: Baby Plum, Bumbino, Reap Creep, and The Pile.
    • Baby Plum has a Delirium form, but Bumbino, Reap Creep, and The Pile are missing one and will simply look like normal.
    • Removed in Repentance Delirium's Hush form can be summoned with 15►Delirious Delirious, but it has to be used many times in quick succession in a same room, which is only possible via cheats or the Debug Console.
    • Delirium can even transform into the hidden incomplete Skinless Hush boss, which does not move and performs basic projectile attacks.
    • Added in Repentance Delirium can transform into a dummy spawned by the spawn dummy command in the Debug Console, and when they do, a functioning endgame chest spawns instantly, which ends the fight and triggers the ending regardless of Delirium's health.
  • There are a couple items themed around Delirium that play off of its ever-changing form - those being 15►Lil Delirium Lil Delirium, 15►Delirious Delirious and Added in Repentance15►D Infinity D Infinity.
  • Added in Repentance Delirium's unlocks for tainted characters mostly reflect the special ability of that character. For example, beating Delirium as Tainted Azazel Tainted Azazel unlocks Added in Repentance15►Hemoptysis Hemoptysis, which gives Isaac the sneeze ability of Tainted Azazel.


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! If Delirium transforms into a segmented boss like Larry Jr. and every segment is killed, the post-boss theme will play as if Delirium has been killed. This may lead to the spawning of hearts as a post-boss reward, making the fight much easier for the player.
Bug Bug! Delirium can transform into Fallen Uriel, Fallen Gabriel, Reap Creep, Bumbino, and The Pile 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 sometimes will not return to normal.
Bug Bug! If Delirious is used to spawn Hush, Delirium will be able to transform into Hush.
Bug Bug! If Delirium transforms into Gemini, Suture will stay in its enraged form separated from Contusion if Delirium transforms to his main form right after transforming into Gemini.
Bug Bug! If Delirium transforms into Blighted Ovum, Suture will keep its usual sprite instead of using its special sprite for Delirium.


Bosses Boss Monstro.png
Chapter 1
Stage Basement icon.pngStage Cellar icon.pngStage Burning Basement icon.png
GeminiStevenBlighted OvumDingleThe Duke of FliesFamineGurglingsThe HauntLarry Jr.MonstroPinWidowThe FallenThe Headless Horseman
DangleLittle HornRag ManTurdlings
Baby Plum
Chapter 1.5
Stage Downpour icon.pngStage Dross icon.png
Lil BlubWormwoodThe RainmakerMin-MinClogColostomiaTurdlet
Chapter 2
Stage Caves icon.pngStage Catacombs icon.pngStage Flooded Caves icon.png
FistulaChubC.H.A.D.Carrion QueenDark OneGurdyGurdy Jr.The HollowThe HuskMega FattyMega MawPeepPestilencePolycephalusThe WretchedThe FallenThe Headless Horseman
The ForsakenThe FrailThe Stain
Big HornRag Mega
Chapter 2.5
Stage Mines icon.pngStage Ashpit icon.png
Reap CreepTuff TwinsHornfelGreat GideonSingeThe ShellThe Pile
Chapter 3
Stage Depths icon.pngStage Necropolis icon.pngStage Dank Depths icon.png
The AdversaryThe BloatThe CageThe GateMonstro IIGishLokiMask of InfamyWarThe FallenThe Headless HorsemanMom
Sisters Vis
Reap CreepThe Pile
Chapter 3.5
Stage Mausoleum icon.pngStage Gehenna icon.png
The SirenThe HereticThe VisageThe Horny BoysMomMom's Heart
Chapter 4
Stage Womb icon.pngStage Utero icon.pngStage Scarred Womb icon.png
BlastocystThe BloatConquestDaddy Long LegsTriachnidDeathLokiiMama GurdyMr. FredScolexTeratomaThe FallenThe Headless HorsemanMom's HeartIt Lives
Sisters VisThe Matriarch
Stage Corpse icon.png
ChimeraThe ScourgeRotgutMother
Chapter 5
Stage Sheol icon.pngStage Cathedral icon.png
Chapter 6
Stage Dark Room icon.pngStage Chest icon.png
???The LambMega Satan
The Void
Stage The Void icon.png
Stage Home icon.png
DogmaThe BeastUltra DeathUltra FamineUltra PestilenceUltra War
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