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

Mom's Knife is an unlockable passive item.


  • Isaac's tears are replaced by a knife that pierces enemies and can travel through obstacles. Holding down the fire button increases its range and power.
    • The knife can hurt enemies while Isaac is holding it.
    • The knife deals 2x Isaac's damage while held and 6x damage at the furthest possible point of its arc, regardless of the actual maximum range stat.
    • Can deal damage 20 times in 1 second upon contact with enemies.
  • Added in Afterbirth This item belongs to the Yes Mother? set. Collecting three items from this set will transform Isaac into his mother.


  • Removed in Repentance Mom's Knife is a special item.
  • The knife can be held and fired diagonally. Firing the knife diagonally requires a frame perfect input. However, this can be done easily with a controller's analog stick or with Added in Afterbirth †15►Analog Stick Analog Stick.
    • Added in Repentance The knife can now be fired in any direction.
  • The knife will not work in challenges with the blindfolded effect.
  • Added in Repentance The knife cannot be used to unlock the door to Mom's Heart in Mausoleum Mausoleum/Gehenna Gehenna .


  • Mom's Knife: Picking up Mom's Knife twice will fire two knives slightly diagonally, similar to The Wiz but closer.
  • 15►20/20 20/20 / Conjoined / 15►The Inner Eye The Inner Eye / 15►Mutant Spider Mutant Spider: Isaac holds only one, but shoots multiple knives at their typical spread.
  • 15►Brimstone Brimstone: Firing the knife also shoots a barrage of knives that goes across the screen, with each knife doing 80% of Isaac's damage. The longer the charge, the more knives are added. This effect does not work with Azazel Azazel's default mini brimstone. The brimstone-knives do not benefit from 15►A Lump of Coal A Lump of Coal.
  • Added in Repentance 15►Compound Fracture Compound Fracture: Creates bone shards while in contact with an enemy.
  • Added in Afterbirth15►Continuum Continuum: The knife can now travel through walls and appear out of the opposite wall but will still have the boomerang effect.
  • Added in Repentance15►Eye Sore Eye Sore: Will occasionally release 1-3 extra knives when shooting Mom's knife.
  • 15►Fire Mind Fire Mind: Still applies burning but no longer explodes.
  • Added in Afterbirth †15►Flat Stone Flat Stone: Knife bounces as it flies away from Isaac, each bounce splash causing Isaac's tear damage.
  • Added in Afterbirth15►Fruit Cake Fruit Cake: The benefits of fruit cake still occur but are short lived due to the high damage of Mom's knife.
  • Added in Afterbirth † The Forgotten The Forgotten: The knife will attach to The Forgotten's bone club, forming a scythe. Increases the size of both the melee swing and the bone throw, and allows a single melee swing to deal damage to an enemy twice instead of just once. +4 damage.
  • Added in Afterbirth †15►Ghost Pepper Ghost Pepper: The flames can shoot from Isaac while holding the fire button.
    • Added in Repentance The flames only shoot when fire button is released.
  • Guppy transformation: Knife hits will rarely spawn a blue fly.
  • Added in Afterbirth † / Removed in Repentance 15►Haemolacria Haemolacria: Haemolacria works at the same time with Mom's Knife, with Haemolacria's fire rate resulting in longer charging.
  • Homing tears: Thrown knives home in on the nearest enemy extremely aggressively. They often stick on the enemy for a while before returning for extra efficiency, but their habit of targeting what's nearest rather than the intended target may also result in extra misses.
  • 15►Ipecac Ipecac: Knife turns green and poison monsters that hit it. Removes Ipecac's damage increase.
    • Added in Afterbirth † / Removed in Repentance Also adds +4 damage.
    • Added in Repentance Damage bonus is +2 damage and the knife explodes on contact.
      • The knife will not explode when held by Isaac without being thrown, or on the return path to Isaac
      • The knife can only explode once during a flight path
  • 15►Lost Contact Lost Contact: The knife will block bullets, even when held (similar to 15►Trinity Shield Trinity Shield but has a smaller blocking area).
  • 15►The Ludovico Technique The Ludovico Technique: Isaac controls a floating knife that does 2x Isaac's damage. Tears stat is ignored and damage is dealt at a rate equivalent of 5 tear delay.
    • The Ludovico Technique + any multi-shot item: Isaac controls a floating knife surrounded by additional rotating knives.
    • The Ludovico Technique + Lost Contact: Floating knife loses almost all ability to block bullets, with a tiny area around the hilt that can stop shots.
    • The Ludovico Technique + 15►Loki's Horns Loki's Horns: Loses Loki's Horns effect; Isaac controls only one floating knife.
    • The Ludovico Technique +15►Brimstone Brimstone: Mom's Knife overrides Brimstone leaving only the floating knife.
  • Added in Afterbirth 15►Monstro's Lung Monstro's Lung: Fires a cluster of 3-5 knives at maximum charge, each dealing 2x damage.
    • With two copies of Monstro's Lung, throws a fan of four extra knives alongside the basic attack regardless of charge.
  • 15►Proptosis Proptosis: The Knife deals double damage regardless of range.
  • 15►Strange Attractor Strange Attractor: Enemies are pulled towards the knife. The effect is minor while not firing and much stronger while the knife is launched.
  • 15►Tammy's Head Tammy's Head: Fires 10 knives in a circle around Isaac, dealing massive damage.
  • Added in Repentance 15►The Parasite The Parasite: Fires two knives in perpendicular directions from the first point of contact with an enemy. Additional knives can also spawn more knives themselves.
  • Tainted Lilith Tainted Lilith: The Gello familiar will carry the knife. When firing once, Gello will not return back to Lilith, instead hanging around stationary. She can drag him around the room and the knife will still deal damage. Pressing any fire button again will whip out Gello, just as normal.
  • Added in Afterbirth / Removed in Repentance 15►Tech X Tech X: Both fire normally.
    • Added in Repentance Overridden by Mom's Knife.
  • 15►Unicorn Stump Unicorn Stump and other invincibility items: Even though the knife cannot be fired, the knife will deal damage while Isaac is invincible.


  • 15►Anti-Gravity Anti-Gravity: Only tear delay down applies.
  • Added in Afterbirth †15►Apple! Apple! / Added in Afterbirth †15►Euthanasia Euthanasia / 15►Tough Love Tough Love: No chance of higher damage or instant kills.
  • 15►Chocolate Milk Chocolate Milk: Doesn't increase damage, but reduces Isaac's tear delay by 20%.
  • 15►Cricket's Body Cricket's Body: Only stat effects apply without splitting.
  • Removed in Repentance Added in Afterbirth †15►Compound Fracture Compound Fracture / 15►The Parasite The Parasite: Only stat effects, if any, apply without splitting.
  • 15►Cursed Eye Cursed Eye: Overridden by Mom's Knife.
  • Removed in Afterbirth / Re-added in Repentance 15►Dr. Fetus Dr. Fetus: Overridden by Mom's Knife.
    • Added in Afterbirth / Removed in Repentance Both the knife and the bombs fire normally.
  • 15►Epic Fetus Epic Fetus: Overridden by Epic Fetus.
    • Added in Afterbirth Each explosion shoots 10 knives in a circle from the point of impact.
  • Added in Afterbirth15►Explosivo Explosivo: Overridden by Mom's Knife.
  • Added in Afterbirth †15►Eye of Belial Eye of Belial: Overridden by Mom's Knife.
  • Added in Repentance15►Eye of the Occult Eye of the Occult: Stat increases/decreases apply, otherwise overridden by Mom's Knife.
  • Guillotine: The knife is fired from the body, not from the head
  • Added in Repentance 15►Haemolacria Haemolacria: Overridden by Mom's Knife.
  • Added in Afterbirth / Removed in Afterbirth † 15►Holy Light Holy Light: Overridden by Mom's Knife.
    • Added in Afterbirth † Holy Light can trigger on both held and thrown knives.
  • Added in Afterbirth † / Removed in Repentance 15►Jacob's Ladder Jacob's Ladder: Overridden by Mom's Knife.
    • Added in Repentance The knife will sometimes generate sparks when hitting an enemy.
  • Added in Afterbirth15►Kidney Stone Kidney Stone: Overridden by Mom's Knife.
  • Added in Afterbirth †15►Lachryphagy Lachryphagy: Overridden by Mom's Knife.
  • Added in Afterbirth †15►Little Horn Little Horn: Works but very rarely.
  • 15►A Lump of Coal A Lump of Coal: No effect on the knife regardless of range.
  • Added in Afterbirth / Removed in Repentance 15►Marked Marked: Only tears up and range up apply.
    • Added in Repentance The knife fires in the direction of the crosshair, charging automatically, with charging time proportionate to the distance of the crosshair from Isaac.
  • 15►Monstro's Lung Monstro's Lung: Overridden by Mom's Knife.
    • Added in Afterbirth Firing a knife causes several other knives to shoot out at random directions.
  • 15►My Reflection My Reflection: No effect.
  • Removed in Afterbirth † 15►Mysterious Liquid Mysterious Liquid: Overridden by Mom's Knife.
    • Added in Afterbirth † The Knife leaves creep trails while fired.
  • Added in Repentance15►Saturnus Saturnus: No effect for Orbiting tears.
  • Added in Afterbirth †15►Pop! Pop!: Overridden by Mom's Knife.
  • Added in Afterbirth15►Pupula Duplex Pupula Duplex: Overridden by Mom's Knife.
  • 15►Rubber Cement Rubber Cement: Overridden by Mom's Knife.
  • Tainted Azazel Tainted Azazel: Unlike normal Brimstone, T. Azazel does not get the synergy, and instead Mom's Knife will override his thin Brimstone.
  • Removed in Afterbirth † / Re-added in Repentance 15►Technology Technology: Overridden by Mom's Knife.
    • Added in Afterbirth † / Removed in Repentance Both the knife and the laser fire normally.
  • 15►Tiny Planet Tiny Planet: Knives go in a spiral around Isaac; the longer the knife is charged, the bigger the spiral. Removed in RepentanceNot recommended, as this makes Mom's Knife almost impossible to aim.
    • Mom's Knife will orbit Isaac incredibly fast, dealing consistent damage and covering every side of Isaac.
  • Added in Afterbirth15►Tractor Beam Tractor Beam: The knife will snap to whichever direction Isaac is firing in after it's thrown. However, it can no longer be fired diagonally.
  • Added in Afterbirth †15►Trisagion Trisagion: Overridden by Mom's Knife.
  • 15►Tech X Tech X: Overridden by Mom's Knife.

In-game Footage[]


  • Added in Afterbirth This item is used in I RULE! (challenge #26).
  • In the original Binding of Isaac, buying the item from the Devil Room cost 1 Red Heart container instead of 2.
  • In the original Binding of Isaac, this item gave Isaac the appearance of his mother in her dress, like Yes Mother? transformation.
  • The description of the item is a possible reference to one of the Sniper's dialogue when performing the Huntsman taunt in Team Fortress 2.



PC QQ4A Z0NY (Treasure room adjacent to spawn)

PC Added in Afterbirth † Normal and hard modes only WMB8 QEK8 (Treasure Room adjacent to spawn)

PC Added in Afterbirth † 6PG9 7RK3 (Treasure Room up and to the right one room from spawn)

PC Added in Afterbirth DVNV YV9Y (Treasure Room adjacent to spawn)

PC JW43 H8EK (Treasure Room adjacent to spawn)

PC 1M9E Y1G1 (Treasure Room adjacent to spawn)

PC P8SE A9JW (Treasure Room adjacent to spawn)

PS4 S63T 434W (Treasure Room adjacent to spawn)

Switch Greedier mode only JZCL 97JE (First Golden Treasure Room)

3DS Hard mode only Z3SL DS3W (First floor Treasure Room)


Bug Bug! The Blindfolded condition also applies to the knives fired by Tammy's Head, and prevents it from working.
Bug Bug! The 15►Tiny Planet Tiny Planet and Homing tears may cause a visual bug when there is a high range. This makes it look like the knife is going in circles, when its not rotating around the body.
Bug Bug! Using Mom's Knife and Marked with Haemolacria will cause it to only fire towards the center of room, using the fire buttons will barely move the Marked icon; while Mom's Knife will be unusable and locked to the right.

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