- 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.
- 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.
- Can deal damage 20 times in 1 second upon contact with enemies.
- This item belongs to the Yes Mother? set. Collecting three items from this set will transform Isaac into his mother.
- 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 Analog Stick.
- The knife can now be fired in any direction.
- The knife will not work in challenges with the blindfolded effect.
- The knife cannot be used to unlock the door to Mom's Heart in Mausoleum/ Gehenna .
- 20/20 / Conjoined / The Inner Eye / Mutant Spider: Isaac holds only one, but shoots multiple knives at their typical spread.
- Brimstone: Firing the knife also shoots a barrage of knives that goes across the screen, with each knife doing 80% of (2x) Isaac's damage. The longer the charge, the more knives are added. This effect does not work with Azazel's default mini brimstone. The brimstone-knives do not benefit from A Lump of Coal. Using Sulfur also grants this effect.
- Continuum: The knife can now travel through walls and appear out of the opposite wall but will still have the boomerang effect.
- Eye Sore: Will occasionally release 1-3 extra knives when shooting Mom's knife.
- Fire Mind: Still applies burning but no longer explodes.
- Flat Stone: Knife bounces as it flies away from Isaac, each bounce splash causing Isaac's tear damage.
- Fruit Cake: The benefits of fruit cake still occur but are short lived due to the high damage of Mom's knife.
- 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.
- Ghost Pepper: The flames can shoot from Isaac while holding the fire button.
- The flames only shoot when fire button is released.
- Guppy transformation: Knife hits will rarely spawn a blue fly.
- Knife hits spawn blue flies much more frequently.
- Haemolacria: Haemolacria works at the same time with Mom's Knife, with Haemolacria's fire rate resulting in longer charging.
- Overridden by Mom's Knife.
- 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.
- Ipecac: Knife turns green and poison monsters that hit it. Removes Ipecac's damage increase.
- Also adds +4 damage.
- 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
- 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.
- 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.
- Proptosis: The Knife deals double (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: 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.
- Tech X: Both fire normally.
- Overridden by Mom's Knife.
- Unicorn Stump and other invincibility items: Even though the knife cannot be fired, the knife will deal damage while Isaac is invincible.
- Anti-Gravity: Only tear delay down applies.
- Apple! / Euthanasia / Tough Love: No chance of higher damage or instant kills.
- Chocolate Milk: Doesn't increase damage, but reduces Isaac's tear delay by 20%.
- Cricket's Body: Only stat effects apply without splitting.
- Compound Fracture / The Parasite: Only stat effects, if any, apply without splitting.
- Compound Fracture now creates bone shards while in contact with an enemy.
- The Parasite now fires two knives in perpendicular directions from the first point of contact with an enemy. Additional knives can also spawn more knives themselves.
- Cursed Eye: Overridden by Mom's Knife.
- Dr. Fetus: Overridden by Mom's Knife.
- Both the knife and the bombs fire normally.
- Epic Fetus: Overridden by Epic Fetus.
- Each explosion shoots 10 knives in a circle from the point of impact.
- Explosivo: Overridden by Mom's Knife.
- Eye of Belial: Overridden by Mom's Knife.
- 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.
- Holy Light: Overridden by Mom's Knife.
- Holy Light can trigger on both held and thrown knives.
- Jacob's Ladder: Overridden by Mom's Knife.
- The knife will sometimes generate sparks when hitting an enemy.
- Kidney Stone: Overridden by Mom's Knife.
- Lachryphagy: Overridden by Mom's Knife.
- Little Horn: Works but very rarely.
- A Lump of Coal: No effect on the knife regardless of range.
- Marked: Only tears up and range up apply.
- The knife fires in the direction of the crosshair, charging automatically, with charging time proportionate to the distance of the crosshair from Isaac.
- Monstro's Lung: Overridden by Mom's Knife.
- Firing a knife causes several other knives to shoot out at random directions.
- My Reflection: No effect.
- Mysterious Liquid: Overridden by Mom's Knife.
- The Knife leaves creep trails while fired.
- Saturnus: No effect for Orbiting tears.
- Pop!: Overridden by Mom's Knife.
- Pupula Duplex: Overridden by Mom's Knife.
- Rubber Cement: Overridden by Mom's Knife.
- Tainted Azazel: Unlike normal Brimstone, T. Azazel does not get the synergy, and instead Mom's Knife will override his thin Brimstone.
- Technology: Overridden by Mom's Knife.
- Both the knife and the laser fire normally.
- Tiny Planet: Knives go in a spiral around Isaac; the longer the knife is charged, the bigger the spiral. Not 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.
- 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.
- Trisagion: Overridden by Mom's Knife.
- 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 6PG9 7RK3 (Treasure Room up and to the right one room from spawn)
PC 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)
|Bug!||The Blindfolded condition also applies to the knives fired by Tammy's Head, and prevents it from working.|
|Bug!||The 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!||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.|
|The Binding of Isaac: Rebirth|
|Achievements||Attributes||Bosses||Cards and Runes||Challenges||Chapters|