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This article contains all information from the original The Binding of Isaac game as well as two DLCs. It includes information about characters, items, monsters, bosses, chapters, etc. that first appear in the original game.

Note: This article is still under construction.


Wrath of the Lamb


Monstro is a slow-moving but hard-hitting boss. He is commonly encountered in the The Basement.


He will semi-randomly switch between hopping towards the character, spitting a burst of blood tears (noticed by his "about-to-sneeze" expression), or launch into the air and land at the spot the player was standing in when he went up along with blood shots fired in many directions when he hits the ground. 

  • The distance between the character and Monstro will not influence the attack he will choose, he switches between them at will. Therefore, they'll want to stay at medium range to retain maximum flexibility. The blood shot spray looks nasty, but the shots have arcs that often go over their head.
  • It's also possible to circle around Monstro while staying at a short distance. This way, they don't have to worry about his shots, but his small leaps become a bit more dangerous.
  • Despite his bulk, Monstro moves around a fair bit; area of effect items (like Mr. Boom, Lemon Mishap, or Doctor's Remote) will not be very effective unless they get lucky on placement. Doctor's Remote, however, works somewhat well as the player can use mouse clicks to stay on target with Monstro. Try to wait until he launches into the air, then move and aim where they were standing when he lept. Use his shadow to track where he will land.
  • Regular bombs take large chunks out of his health, but if he decides to launch you may end up wasting the bomb. An easy way to use area of effect items is when Monstro makes a huge jump, he will land approximately at your last position before he jumped, so just use the item before moving.
  • If Isaac is down to one heart, avoiding damage becomes a number-one priority as some of Monstro's shots (the bigger ones) can deal up to a full heart of damage.
  • For some people, it's hard to tell where he is when jumping in the air, so homing shots can help to predict his landing. Isaac can sometimes tell by the shadow that Monstro's body makes in where he will land, but mainly, he only lands where Isaac current position was/is.
  • It's possible to run underneath Monstro while he is "hopping". This can make shooting a bit easier.
  • Pay attention. If Monstro uses his blood spray while Isaac is cornered, look for an opening. There's an opening in every barrage Monstro throws at him, so use this to Isaac's advantage.

Champion Variants


Red Monstro

This version is much smaller and has less health. An additional Monstro shows up, and you'll have to battle both of them simultaneously. In boss rooms, there will be two and in normal rooms in later levels, one will be added to the amount that would spawn in the room by default. Obviously, when smaller, it's harder to stay still and maintain fire, and with two or three of them present, it's best to run in a circle around them and never fully stop moving unless they're both just hopping around.


Monstro alt Black

This champion is slightly larger and has more health. He can't launch himself into the air, and uses his shot attacks much more often.


Appears during Hard Mode, Monstro vomit lasts longer, shooting more disorganized projectiles. Similar to Blastocyst, he splits into 2, each splitting into 2 more before his defeat.


  • Monstro appears in the demo.
  • It is possible to have Monstro shove the character out of the boss room. If he lands on them when they're next to the boss door, they can sometimes clip through it. (Only proven with original game without the Wrath of the Lamb DLC.)

Wrath of the Lamb

The Blighted Ovum is the posthumous version of Gemini appearing in the Catacombs and, rarely, in the Cellar. He has a higher chance of appearing if Isaac has killed Gemini before.

The Blighted Ovum spawns already separated, similar to the green Champion version of Gemini.


The larger sibling appears as a mangled and bloody zombie, with parts of the skull eaten away. He leaves behind a trail of red creep as he moves, which damages Isaac for a full heart. Unlike Gemini, he will constantly pursue Isaac, not stopping for breath after charging.

Meanwhile, the other half appears as an invulnerable spirit, and is passive unless Isaac gets in his line of sight, in which case, he fires a blood beam similar to Brimstone. He tends to stay floating in the area it spawns in, not moving around much. 

Upon death, each half shoots radial blood shots, similar to when Steven is killed.


Wrath of the Lamb


Mulligans are weak monsters that first appear in Chapter 1.


Mulligans attempt to avoid the player as much as possible, and may even run over spikes or into fires in doing so. They don't damage the player on touch, but staying close to them is very unwise: they may commit suicide and explode (like Mulligoons) and leave 4 projectiles travelling orthogonally along with 2-4 random flies (Pooter, red and black Flies).


Mulligan as shown on Isaac's Last Will.

They are sometimes replaced by their gray-colored counterparts, known as Mulligoons, but they can be seen in the same room together.

The chance of them killing becomes higher when they're in corners.

Embryos are monsters appearing in Chapter 1 and 4.


Embryos are completely harmless. They hop around aimlessly and never target Isaac, but can still deal contact minimal damage. This enemy can spawn on any floor and is usually met in a room with a Blood Donation Machine.

Vis is a monster that first appear in Chapter 3.


Vis walk a bit slow around in the room aimlessly. When lined up with Isaac (horizontally or vertically), Vis will begin shaking violently and then fire a wide blood beam (similar to Brimstone) from their stomach for a few seconds. This blood beam may still damage Isaac for a fraction of a second after the beam has disappeared, so be careful.


  • If the player has Wrath of the Lamb DLC installed, Vis may turn into Double Vis for a few frames when firing their blood beam.

Babies are floating, infant-like monsters first encountered in Chapter 3.


Babies slowly float towards Isaac, occasionally shooting a single blood shot. They also have the ability to teleport to anywhere in the room, occasionally close to Isaac. They usually teleport after a shot. The only random element is the shooting, and they have no specific cue to indicate incoming attacks.


  • Version 1.33 introduced a bug called "Psy Baby" which was fixed in 1.4.
    • Normal Babies or Angelic Babies could spawn with the ability of firing homing shots similar to the Psychic Maw and the Spoonbender item.


  • If Isaac touch the baby right when it reappears (after disappearing to teleport), he'll take no damage.

Wrath of the Lamb

Angelic Babies are monsters first encountered in Chapter 3.


They are more aggressive than regular Babies. The Angelic Baby fires 3 blood shots at Isaac instead of just 1. When fighting against Isaac, they will shoot regular tears. They also teleport more often, usually near Isaac.


  • Angel Babies will sometimes shoot slowing tears.

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