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 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 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.
    • When transforming into a segmented boss, only the first two segments share Delirium's hp and the other segments have separately generated hp.
    • It can rarely transform into two or even three bosses at once.
    • It can also rarely spawn a separate copy of the boss it transformed into.
    • 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 Added in Repentance Baby Plum Baby Plum, Added in Repentance Bumbino Bumbino, Added in Repentance Reap Creep Reap Creep, and Added in Repentance The Pile The Pile, but only Baby Plum has a unique sprite. Cannot transform into any other Repentance bosses.
    • Added in Repentance Cannot transform into Mega Satan Mega Satan.
  • 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.
    • Destroying non-Delirium segments when he transforms into segmented bosses can also temporarily trigger this effect.
    • If Delirium is being dealt damage at a significantly high rate from multiple tear sources he will attack, teleport, and transform at extreme speeds.

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.
  • Plan C Plan C can be used to kill Delirium. After Plan C is used against Delirium, when pausing in the instant of each flash from Delirium's death animation, the animation can be skipped before the death from Plan C's 3 seconds delay because each flash from Delirium's death animation is still played when the game is paused.[1] It is also recommended to position Isaac on the chest spawn location before Plan C's death occurs.
    • It works with Lazarus' Rags Lazarus' Rags as it revives Isaac on the spot. However, the Completion Mark will go towards Lazarus, not the character originally selected.
    • Added in RepentanceSoul of Lazarus Soul of Lazarus and Added in RepentanceInner 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 RepentanceBirthright 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 mini-bosses.
    • Although Grub 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 at the same time.
    • 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.
  • If a boss earlier in the run is removed via Added in RepentanceEraser Eraser, Delirium will disappear if it attempts to turn into that boss. This will spawn the ending chest and count as having defeated Delirium.
  • Removed in Repentance If Delirium transforms into Mega Satan, the boss maintains the ability to spawn the Harbingers, the Super Sins, and the Fallen Angels, and can do so in quick succession depending on Delirium's health. This can make the fight much longer, as attacking the bosses spawned by Delirium will have no effect on Delirium’s actual health.
  • If Delirium transforms into Isaac and Delirium's health is low enough, it will attempt to perform Isaac's Crack the Sky Crack the Sky attack. However, because Delirium's boss arena is a quadruple-sized room, the attack will cover half of the arena, making it extremely deadly.
  • Each time Delirium transforms, Its Status Effect timer resets, allowing for useful effects to be active for a large portion of the fight if re-inflicted frequently enough.
    • This quirk is especially useful in conjunction the petrification from Mom's Contacts Mom's Contacts, as it can hold delerium in place each time it is petrified, making it a much easier target to hit.


  • 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 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 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 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 Eye 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 Lil' Haunt.
    • Also, if it transformed into Black Champion Brownie when at low health, It would spawn two Dank Squirt 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.
  • 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 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 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.
    • Delirium's Hush form can be summoned with 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.
    • 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 Lil Delirium Lil Delirium, Delirious Delirious and D Infinity D Infinity.
  • Delirium's unlocks for tainted characters mostly reflect the special ability of that character. For example, beating Delirium as Tainted Azazel Tainted Azazel unlocks Hemoptysis Hemoptysis, which gives Isaac the sneeze ability of Tainted Azazel.
    • The only exceptions to this are Tainted Lost Tainted Lost, who instead unlocks Ghost Bombs Ghost Bombs and Tainted Keeper Tainted Keeper, who instead unlocks Keeper's Kin Keeper's Kin.
    • The item that most mimics Tainted Lost's starting ability, Sacred Orb Sacred Orb, is instead unlocked by defeating The Beast.
    • The item that most mimics a Tainted Keeper property is Keeper's Bargain Keeper's Bargain, unlocked by Satan, The Lamb, Isaac and ???'s completion marks together.
  • Prior to patch V1.7.8, Delirium could transform into Mega Satan.


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. This was fixed in patch V1.7.5.
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.
Bug Bug! If Delirium transforms into Blue Champion Larry Jr. it will, due to how Blue Champion Larry Jr.'s HP works, effectively lose a large portion of HP as its total HP will get divided into however many segments it transforms into. It will not receive the lost HP back after transforming again.
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 when Delirium transforms again.
Bug Bug! If Delirium transforms into a doubled champion like pink Polycephalus only one will be Delirium and the other can stay alive and keep fighting like normal
Bug Bug! If Delirium transforms into Blighted Ovum, Suture will keep its usual sprite instead of using its special sprite for Delirium.
Bug Bug! If Delirium transforms into the Mask Of Infamy, It will only transform into the heart.
Bug Bug! If Delirium transforms into The Frail, it will always transform into the first phase, regardless of how much hp it has left (unless it's the Black Champion version).
Bug Bug! If Delirium transforms into Lokii, it will only transform into one Lokii half.
Bug Bug! If Delirium transforms into War's second phase, the body will be invisible (except for when it does its sobbing animation) This also applies to Blighted Ovum Blighted Ovum's Contusion.
Bug Bug! As of patch V1.7.8, if Delirium transforms into a champion boss, it will retain its normal appearance and color, but its attacks (and size in the case of some forms) will be those of the champion.