Binding of Isaac: Rebirth Wiki

Mom's Knife is an unlockable passive item.

Effects[ | ]

  • 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.
  • (except 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.
  • (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.
  • (except in Rebirth) This item belongs to the Yes Mother?Yes Mother? set. Collecting three items from this set will transform Isaac into his mother.

Notes[ | ]

  • (except in Repentance) Mom's Knife is a special item.
  • (except 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 (in Afterbirth † and Repentance)Collectible Analog Stick iconAnalog Stick.
  • (in Repentance) The knife can be held and fired diagonally as if Isaac was holding Collectible Analog Stick iconAnalog 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.

Synergies[ | ]

  • Collectible 20 20 icon20/20 / (except in Rebirth) ConjoinedConjoined / Collectible The Inner Eye iconThe Inner Eye / Collectible Mutant Spider iconMutant Spider: Isaac holds only one, but shoots multiple knives at their typical spread.
  • (in Repentance) Collectible Apple! iconApple! / Collectible Tough Love iconTough Love: The knife deals increased damage sometimes based on luck.
  • Collectible Brimstone iconBrimstone / (in Repentance)Collectible Sulfur iconSulfur: Shooting the knife also shoots a barrage of knives that goes across the screen, with each knife doing 80% ((in Repentance) 2x) of Isaac's damage; the extra knives do not return. The longer the charge, the more knives are added. This effect does not work with Character Azazel iconAzazel's default mini brimstone. The brimstone-knives do not benefit from Collectible A Lump of Coal iconA Lump of Coal.
  • (in Repentance)Collectible Compound Fracture iconCompound Fracture: The knife creates bone shards while in contact with an enemy.
  • (in Repentance)Collectible C Section iconC Section: Fetuses hold small knives that spin around them slowly, causing extra damage.
  • (except in Rebirth)Collectible Diplopia iconDiplopia / (in Afterbirth † and Repentance)Collectible Crooked Penny iconCrooked 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.
  • (except in Rebirth)Collectible Epic Fetus iconEpic Fetus: Each explosion shoots 10 knives in a circle from the point of impact.
  • (in Repentance)Collectible Euthanasia iconEuthanasia / Collectible Little Horn iconLittle Horn: The knife can sometimes instant kill enemies or deal extra damage to bosses.
  • (in Repentance)Collectible Eye Sore iconEye Sore: Will occasionally release 1-3 extra knives when shooting Mom's knife.
  • Collectible Fire Mind iconFire Mind: Still applies burning but no longer explodes.
  • (in Afterbirth † and Repentance)Collectible Flat Stone iconFlat Stone: Knife bounces as it flies away from Isaac, each bounce splash causing Isaac's tear damage.
  • (except in Rebirth)Collectible Fruit Cake iconFruit Cake: The benefits of fruit cake still occur but are short lived due to the high damage of Mom's knife.
  • (in Afterbirth † and Repentance) Character The Forgotten iconThe 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.
  • (in Afterbirth †)Collectible Ghost Pepper iconGhost Pepper: The flames can shoot from Isaac while holding the fire button.
    • (in Repentance) The flames only shoot when fire button is released.
  • (except in Repentance) GuppyGuppy: Knife hits will rarely spawn a blue fly.
    • (in Repentance) Knife hits will frequently spawn a blue fly.
  • (in Afterbirth † and Repentance)Collectible Holy Light iconHoly Light: Holy Light can trigger on both held and thrown knives.
  • (except in Afterbirth †)Collectible Ipecac iconIpecac: Knife turns green and poison monsters that hit it. Removes Ipecac's damage increase.
    • (in Afterbirth †) Adds a flat +4 damage instead of Ipecac's +40. Knife turns green and poison monsters that hit it.
    • (in Repentance) Adds a flat +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. Knife turns green and poison monsters that hit it.
      • (in Repentance) Ipecac + Collectible Technology iconTechnology: Not recommended. Isaac will always take explosion damage when throwing the knife.
  • Invulnerability: Even though the knife cannot be fired, the knife will deal damage while Isaac is invincible.
  • (in Repentance)Collectible Jacob's Ladder iconJacob's Ladder: The knife will sometimes generate sparks when hitting an enemy.
  • (in Afterbirth † and Repentance)Collectible Little Horn iconLittle Horn: Works but very rarely.
  • (except in Repentance)Collectible Lost Contact iconLost Contact: The knife will block bullets, even when held (similar to Collectible Trinity Shield iconTrinity Shield but has a smaller blocking area).
  • Collectible The Ludovico Technique iconThe 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.
      • Losing The Ludovico Technique will leave the additional knives, which are no longer controlled and appear in the same spot in every room.
    • (except in Repentance) The Ludovico Technique + Collectible Lost Contact iconLost Contact: Floating knife loses almost all ability to block bullets, with a tiny area around the hilt that can stop shots.
    • The Ludovico Technique + Collectible Loki's Horns iconLoki's Horns: Loses Loki's Horns effect; Isaac controls only one floating knife.
    • The Ludovico Technique + Collectible Brimstone iconBrimstone: Mom's Knife overrides Brimstone leaving only the floating knife.
  • (in Repentance)Collectible Marked iconMarked: The knife fires in the direction of the crosshair, charging automatically, with charging time proportionate to the distance of the crosshair from Isaac.
  • Collectible Mom's Eye iconMom's Eye: Another knife is permanently behind Isaac, able to deal contact damage. The fire chance is still affected by luck as usual.
  • (except in Rebirth)Collectible Monstro's Lung iconMonstro's Lung: Firing a knife causes several other knives to shoot out in random directions.
  • (in Afterbirth † and Repentance)Collectible Mysterious Liquid iconMysterious Liquid: The knife leaves creep trails while fired.
  • (in Repentance)Collectible The Parasite iconThe 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.
    • The Parasite + Collectible Technology iconTechnology: Lasers will also split with the knives.
  • (in Afterbirth † and Repentance)Collectible Pause iconPause: Mom's Knife will not stop the pause effect allowing Isaac to kill or chip bosses easily by standing near them for the duration of the pause effect.
  • (except in Repentance)Collectible Proptosis iconProptosis: The Knife deals double damage regardless of range.
    • (in Repentance) The Knife deals triple damage regardless of range.
  • (in Repentance)Collectible Spirit Sword iconSpirit Sword: Allows the spirit sword to be thrown during charged attacks.
  • Collectible Strange Attractor iconStrange Attractor: Enemies are pulled towards the knife. The effect is minor while not firing and much stronger while the knife is launched.
  • (in Repentance) Character Tainted Lilith iconTainted 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.
  • (in Afterbirth †)Collectible Technology iconTechnology Both the knife and the laser fire normally.
    • (in Repentance) There is a connecting laser between Isaac and the knife, similar to Character The Forgotten iconThe Forgotten's club throw.
  • (in Afterbirth †)Collectible Tech X iconTech X: Both fire normally.
    • (in Repentance) The knife is fired with a Tech X ring around it, similarly to Character The Forgotten iconThe Forgotten's club throw.
  • (except in Rebirth)Collectible The Wiz iconThe Wiz: Isaac holds two knives. Knives are shot diagonally.

Interactions[ | ]

Overridden by Mom's Knife:

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

Other interactions:

  • (except in Repentance)Collectible Chocolate Milk iconChocolate Milk: Doesn't increase damage, but reduces Isaac's tear delay by 20%.
  • (in Rebirth)Collectible Epic Fetus iconEpic Fetus: Overridden by Epic Fetus.
  • Collectible Guillotine iconGuillotine: The knife is fired from the body, not from the head.
  • (in Afterbirth †)Collectible Haemolacria iconHaemolacria: Both apply normally; the tears down negatively affects Mom's Knife's charge time.
  • (in Repentance)Collectible Saturnus iconSaturnus: No effect for orbiting tears.
  • Collectible Tammy's Head iconTammy's Head: Fires 10 knives in a circle around Isaac, doesn't add Tammy's Head's flat damage bonus.
  • Collectible Tiny Planet iconTiny Planet: The knife goes in a spiral around Isaac; the longer the knife is charged, the bigger the spiral. (except in Repentance) Not recommended, as this makes Mom's Knife almost impossible to aim.
    • (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 Collectible Brimstone iconBrimstone or Collectible Monstro's Lung iconMonstro's Lung, will cause the knives to circle around Isaac once, then shoot out in the intended direction in a straight line.
  • (except in Rebirth)Collectible Tractor Beam iconTractor 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[ | ]

Trivia[ | ]

  • This item is used in (except in Rebirth) I RULE! (challenge #26).
  • In the original The Binding of Isaac, buying the item from the Devil RoomDevil 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.
  • 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.

Gallery[ | ]

Bugs[ | ]

Bug Bug! Collectible Tiny Planet iconTiny 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 Collectible Tiny Planet iconTiny 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! (in Afterbirth †) Using Mom's Knife and Collectible Marked Afterbirth iconMarked with Collectible Haemolacria iconHaemolacria 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! (except in Repentance) The Blindfolded condition also applies to the knives fired by Collectible Tammy's Head iconTammy's Head, and prevents it from working.