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 deals damage 20 times per second upon contact with enemies while Isaac is holding it.
  • Removed in Repentance The knife deals 2x Isaac's damage while held and 6x damage at the furthest possible point of its throw distance, regardless of the actual maximum range stat.
  • Added in Repentance Damage dealt by the knife depends on its charge state. The knife deals 2x Isaac's damage when held and 6x damage at about 1/3 of full charge. The knife damage quickly drops to 2x Isaac's damage when returning regardless of charge state. Further charging only increases its maximum range.
  • 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.
  • Removed in Repentance The knife can be held and fired diagonally with frame perfect input. This can be done easily with a controller's analog stick or with Added in Afterbirth †Analog Stick Analog Stick.
  • Added in Repentance The knife can be held and fired diagonally as if Isaac was holding Analog Stick Analog Stick.
    • The knife can be fired in any direction if using mouse controls (enabled in options.ini).
  • The knife will not work in challenges with the blindfolded effect.


  • 20/20 20/20 / Conjoined / The Inner Eye The Inner Eye / Mutant Spider Mutant Spider: Isaac holds only one, but shoots multiple knives at their typical spread.
  • Added in Repentance Apple! Apple!/Tough Love Tough Love: The knife deals increased damage sometimes based on luck.
  • Brimstone Brimstone / Added in RepentanceSulfur Sulfur: Firing the knife also shoots a barrage of knives that goes across the screen, with each knife doing 80% of (Added in Repentance2x) Isaac's damage; the extra knives do not return. 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 A Lump of Coal A Lump of Coal.
  • Added in Repentance Compound Fracture Compound Fracture: The knife creates bone shards while in contact with an enemy.
  • Added in RepentanceC Section C Section: Fetuses hold small knives that spin around them slowly, causing extra damage.
  • Added in AfterbirthDiplopia Diplopia/Added in Afterbirth †Crooked Penny Crooked Penny: Each additional copy of the item will grant an extra knife that fires slightly diagonally from the original one, up to a maximum of 16. Picking up more than 16 knives won't fire more knives but will still modify the angle at which they're shot.
  • Added in Afterbirth Epic Fetus Epic Fetus: Each explosion shoots 10 knives in a circle from the point of impact.
  • Added in Repentance Euthanasia Euthanasia: The knife sometimes deals higher damage, but instant kill ability is overridden.
  • Added in RepentanceEye Sore Eye Sore: Will occasionally release 1-3 extra knives when shooting Mom's knife.
  • Fire Mind Fire Mind: Still applies burning but no longer explodes.
  • Added in Afterbirth †Flat Stone Flat Stone: Knife bounces as it flies away from Isaac, each bounce splash causing Isaac's tear damage.
  • Added in AfterbirthFruit 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: +4 damage. 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.
  • Added in Afterbirth † / Removed in Repentance 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.
  • Removed in Repentance Guppy transformation: Knife hits will rarely spawn a blue fly.
  • Added in Repentance Guppy transformation: Knife hits will frequently spawn a blue fly.
  • Added in Afterbirth † Holy Light Holy Light: Holy Light can trigger on both held and thrown knives.
  • Removed in Afterbirth † / Re-added in Repentance 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 Adds +2 damage and the knife explodes on contact, once per throw. Will not explode while held without throwing and while coming back to the Player after being thrown.
  • Invulnerability: Even though the knife cannot be fired, the knife will deal damage while Isaac is invincible.
  • Added in Repentance Jacob's Ladder Jacob's Ladder: The knife will sometimes generate sparks when hitting an enemy.
  • Lost Contact Lost Contact: The knife will block bullets, even when held (similar to Trinity Shield Trinity Shield but has a smaller blocking area).
  • 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 + Loki's Horns Loki's Horns: Loses Loki's Horns effect; Isaac controls only one floating knife.
    • The Ludovico Technique + Brimstone Brimstone: Mom's Knife overrides Brimstone leaving only the floating knife.
  • Added in Repentance Marked Marked: The knife fires in the direction of the crosshair, charging automatically, with charging time proportionate to the distance of the crosshair from Isaac.
  • Added in Afterbirth Monstro's Lung Monstro's Lung: Firing a knife causes several other knives to shoot out in random directions.
  • Added in Afterbirth † Mysterious Liquid Mysterious Liquid: The knife leaves creep trails while fired.
  • Added in Repentance The Parasite The Parasite: The knife fires two knives in perpendicular directions from the first point of contact with an enemy. Additional knives can also fire more knives themselves.
  • Removed in Repentance Proptosis Proptosis: The Knife deals double damage regardless of range.
    • Added in Repentance The Knife deals triple damage regardless of range.
  • 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.
  • Tammy's Head Tammy's Head: Fires 10 knives in a circle around Isaac, dealing massive damage.
  • Added in Repentance Tainted Lilith Tainted Lilith: Her 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 Technology Technology Both the knife and the laser fire normally.
    • Added in Repentance There is a connecting laser between Isaac and the knife, similar to The Forgotten The Forgotten's club throw.
  • Removed in Afterbirth / Re-added in Afterbirth † / Re-removed in Repentance Added in Afterbirth †Tech X Tech X: Both fire normally.
    • Added in Repentance The knife is fired with a Tech X ring around it, similarly to The Forgotten The Forgotten's club throw.


Overridden by Mom's Knife:

Only stat effects are applied; otherwise overridden by Mom's Knife:

Other interactions:

  • Removed in RepentanceChocolate Milk Chocolate Milk: Doesn't increase damage, but reduces Isaac's tear delay by 20%.
  • Removed in Afterbirth Epic Fetus Epic Fetus: Overridden by Epic Fetus.
  • Guillotine Guillotine: The knife is fired from the body, not from the head.
  • Added in Afterbirth † / Removed in Repentance Haemolacria Haemolacria: Both apply normally; the tears down negatively affects Mom's Knife's charge time.
  • Added in Afterbirth †Little Horn Little Horn: Works but very rarely.
  • Added in RepentanceSaturnus Saturnus: No effect for orbiting tears.
  • Tiny Planet Tiny Planet: The knife goes in a spiral around Isaac; the longer the knife is charged, the bigger the spiral. Removed in Repentance Not recommended, as this makes Mom's Knife almost impossible to aim.
    • Added in Repentance Launched knife will orbit Isaac incredibly fast with a much larger hitbox, dealing consistent damage and covering every side of Isaac.
    • Items that fire knives out in a straight line, like Brimstone Brimstone or Monstro's Lung Monstro's Lung, will cause the knives to circle around Isaac once, then shoot out in the intended direction in a straight line.
  • Added in AfterbirthTractor 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.

In-game Footage[]


  • Added in Afterbirth This item is used in I RULE! (Challenge #26).
  • In the original The Binding of Isaac, buying the item from the Devil Room cost 1 Red Heart container instead of 2.
  • In the original The 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 Added in Repentance QQ4A Z0NY (Treasure Room Treasure Room adjacent to spawn)

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

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

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

PC JW43 H8EK (Treasure Room Treasure Room adjacent to spawn)

PC 1M9E Y1G1 (Treasure Room Treasure Room adjacent to spawn)

PC P8SE A9JW (Treasure Room Treasure Room adjacent to spawn)

PS4JJTP S7AY (Treasure Room Treasure Room adjacent to spawn)

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

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


Bug Bug! 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! With Tiny Planet Tiny Planet, if Isaac releases the knife and exit the room before it returns to him, the knife will receive a significantly larger hitbox that scales with Isaac's Range. Releasing it and waiting until it returns will make it normal again.
Bug Bug! Added in Afterbirth † / Removed in Repentance Using Mom's Knife and Marked Marked with Haemolacria Haemolacria will cause the latter to only fire towards the center of room. Using the fire buttons will barely move the Marked crosshair, while Mom's Knife will be unusable and locked to the right.
Bug Bug! Removed in Repentance The Blindfolded condition also applies to the knives fired by Tammy's Head Tammy's Head, and prevents it from working.