Mom's Knife

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.
• 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 instead of its actual range. 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.

Notes

• (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 †) 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.

Synergies

• 20/20 / Conjoined / The Inner Eye / Mutant Spider: Isaac holds only one, but shoots multiple knives at their typical spread.
• Brimstone / (Added in Repentance) Sulfur: Firing the knife also shoots a barrage of knives that goes across the screen, with each knife doing 80% of ((Added in Repentance)2x) 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.
• (Added in Repentance) C Section: Fetuses hold small knives that spin around them slowly, causing extra damage.
• (Added in Repentance) Eye Sore: Will occasionally release 1-3 extra knives when shooting Mom's knife.
• Fire Mind: Still applies burning but no longer explodes.
• (Added in Afterbirth †) Flat Stone: Knife bounces as it flies away from Isaac, each bounce splash causing Isaac's tear damage.
• (Added in Afterbirth) 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.
• (Removed in Repentance) 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 (Removed in Repentance) rarely/(Added in Repentance) frequently spawn a blue fly.
• (Removed in Afterbirth † / Re-added in Repentance) 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.
• Lost Contact: The knife will block bullets, even when held (similar to Trinity Shield but has a smaller blocking area).
• 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: Loses Loki's Horns effect; Isaac controls only one floating knife.
  • The Ludovico Technique + Brimstone: Mom's Knife overrides Brimstone leaving only the floating knife.
• Mom's Knife: 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.
• Proptosis: The Knife deals double ((Added in Repentance) triple) damage regardless of range.
• 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: Fires 10 knives in a circle around Isaac, dealing massive damage.
• (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.
• Unicorn Stump and other invincibility items: Even though the knife cannot be fired, the knife will deal damage while Isaac is invincible.

Interactions

Overridden by Mom's Knife:

• (Azazel) Azazel's default attack
• Cursed Eye
• (Removed in Afterbirth / Re-added in Repentance) Dr. Fetus
  • (Added in Afterbirth / Removed in Repentance) Both the knife and the bombs fire normally.
• (Added in Afterbirth † / Removed in Repentance) Euthanasia
  • (Added in Repentance) Sometimes deals higher damage, but instant kill ability is overridden.
• (Added in Afterbirth) Explosivo
• (Added in Afterbirth †) Eye of Belial
• (Added in Repentance) Haemolacria
  • (Added in Afterbirth † / Removed in Repentance) Both apply normally; the tears down negatively affects Mom's Knife's charge time.
• (Added in Afterbirth / Removed in Afterbirth †) Holy Light
  • (Added in Afterbirth †) Holy Light can trigger on both held and thrown knives.
• (Added in Afterbirth) Kidney Stone
• (Added in Afterbirth †) Lachryphagy
• A Lump of Coal
• (Added in Afterbirth †) Pop!
• (Added in Afterbirth) Pupula Duplex
• (Added in Afterbirth † / Removed in Repentance) Jacob's Ladder
  • (Added in Repentance) The knife will sometimes generate sparks when hitting an enemy.
• (Removed in Afterbirth) Monstro's Lung
  • (Added in Afterbirth) Firing a knife causes several other knives to shoot out at random directions.
• (Removed in Afterbirth †) Mysterious Liquid
  • (Added in Afterbirth †) The Knife leaves creep trails while fired.
• (Added in Afterbirth †) Parasitoid
• Rubber Cement
• (Tainted Azazel) Tainted Azazel's default attack
• (Removed in Afterbirth † / Re-added in Repentance) Technology
  • (Added in Afterbirth † / Removed in Repentance) Both the knife and the laser fire normally.
  • (Added in Repentance) There is a connecting laser between Isaac and the knife, similarly to the forgotten's club throw
• (Added in Repentance) Tech X
  • (Added in Afterbirth / Removed in Repentance) Both fire normally.
  • (Added in Repentance) The knife is fired with a Tech X ring around it, similarly to the forgotten's club throw.
• (Added in Afterbirth † / Removed in Repentance) Tough Love
• (Added in Afterbirth †) Trisagion

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

• Anti-Gravity
• (Added in Afterbirth † / Removed in Repentance) Apple!
  • (Added in Repentance) The knife deals quadruple damage sometimes based on luck.
• (Added in Afterbirth † / Removed in Repentance) Compound Fracture
  • (Added in Repentance) Now creates bone shards while in contact with an enemy.
• Cricket's Body
• (Added in Repentance) Eye of the Occult
• (Added in Afterbirth / Removed in Repentance) Marked
  • (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.
• My Reflection
• (Removed in Repentance) The Parasite
  • (Added in Repentance) Now fires two knives in perpendicular directions from the first point of contact with an enemy. Additional knives can also fire more knives themselves.

Other interactions:

• Chocolate Milk: Doesn't increase damage, but reduces Isaac's tear delay by 20%.
• Epic Fetus: Overridden by Epic Fetus.
  • (Added in Afterbirth) Each explosion shoots 10 knives in a circle from the point of impact.
• Guillotine: The knife is fired from the body, not from the head.
• (Added in Afterbirth †) Little Horn: Works but very rarely.
• (Added in Repentance) Saturnus: No effect for Orbiting tears.
• 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 or 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 Afterbirth) 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.