Mom's Knife

Mom's Knife is a Special 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 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.

Synergies

 * : 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's default mini brimstone. The brimstone-knives do not benefit from.
 * : Tears up instead of additional damage or charge effects. Knife will also be colored brown.
 * : The knife can now travel through walls and appear out of the opposite wall but will still have the boomerang effect.
 * : No effect.
 * Each explosion shoots 10 knives in a circle from the point of impact.
 * : Damage is doubled. However, the knife takes longer to charge.
 * : Still applies burning but no longer explodes.
 * : Knife bounces as it flies away from and towards Isaac.
 * : The flames can shoot from Isaac while holding the fire button.
 * : The held knife can damage enemies while Isaac is invincible.
 * : The knife homes in on enemies, but it does not gain a damaging halo.
 * Guppy Transformation: Knife hits will rarely spawn an attack fly.
 * Bookworm Transformation: 2 knives occasionally (based on luck) will fire forward in the direction aimed, splitting apart in trajectory slightly.
 * : Haemolacria works with minimal tear delay while Mom's Knife has to be charged.
 * Homing Tears: Knives home in on enemies and colors the knife purple. It will stick on enemies for a second and make small lunges towards other enemies.
 * The Forgotten: The knife attaches to the Forgotten's bone club, forming a scythe with a larger swing and higher damage.
 * : Isaac holds only one, but shoots three knives. Slower charge time.
 * : Knife turns green and may poison monsters that hit it.
 * Also adds +4 damage.
 * : Adds three knives in the other directions that the primary knife is facing. These knives will sometimes fire when the primary knife is fired. This is affected by luck; the higher Isaac's luck is, the higher the chance the other knives will fire as well. Like the primary knife, they can be used as melee weapons.
 * : The knife will block bullets, even when held. Furthermore, the knife will not vanish after canceling a bullet, and therefore can cancel out several bullets at once while being shot or held.
 * : Isaac controls a floating knife that deals 2x Isaac's damage. Tears stat is ignored and damage is dealt at a rate equivalent of 5 tear delay.
 * + : Isaac controls a floating knife surrounded by 1 rotating knife.
 * + : Isaac controls a floating knife surrounded by 2 rotating knives.
 * + : Isaac controls a floating knife surrounded by 3 rotating knives.
 * + : Floating knife loses almost all ability to block bullets. Only blocks shots that cross a very specific, small point on the knife. (Seems to be close to where hilt meets blade on the sprite.)
 * + : Loses Loki's Horns effect; Isaac controls only one floating knife.
 * : Adds a second knife in the opposite direction that the primary knife is facing. This knife can sometimes fire when the primary knife is fired. This is affected by luck; the higher Isaac's luck is, the higher the chance the other knife will fire as well. Like the primary knife, it can be used as a melee weapon.
 * + : Results in a total of four knives like Loki's Horns on its own, but the secondary knives fire with the same frequency that the single Mom's Eye knife would.
 * : If picked up twice in the same run, two knives are fired at once.
 * : Fires a cluster of 3-5 knives at maximum charge, each dealing 2x damage.
 * : Isaac holds only one, but shoots four knives. Slower charge time.
 * + : Isaac shoots seven knives.
 * : No effect.
 * Poison Tears: Knives gain a chance to poison enemies.
 * : The Knife deals double damage regardless of range.
 * : Enemies and pickups are attracted to the knife, even when not charging or firing.
 * : Fires 10 knives in a circle around Isaac, dealing massive damage.
 * : Both fire normally.
 * : Both fire normally.
 * : While charging Mom's Knife, Technology 2 will still fire.
 * : Blocks bullets in the direction the knife is held, giving enough protection to walk up to and melee enemies, or just to safely shoot the knife.
 * and other invincibility items: Even though the knife cannot be fired, the knife will deal damage while Isaac is invincible.
 * : Grants two knives that fire diagonally.

Interactions

 * : Only tear delay down applies.
 * : Overridden by Mom's Knife.
 * : Tear delay and range down. No splitting effect.
 * Piercing Tears: No effect.
 * : Overridden by Mom's Knife.
 * : No effect.
 * : Increased damage and decreased tear rate. No scythe visual effect.
 * : Overridden by Mom's Knife.
 * Both the knife and the bombs fire normally.
 * : Overridden by Mom's Knife.
 * : Overridden by Mom's Knife.
 * : Overridden by Mom's Knife.
 * : No effect.
 * : Overridden by Mom's Knife.
 * : Gives no damage boost but colors the knife dark brown.
 * : Only tears up and range up apply.
 * : Overridden by Mom's Knife.
 * Firing a knife causes several other knives to shoot out at random directions.
 * : Overridden by Mom's Knife.
 * : Greatly reduces Mom's Knife range.
 * : Overridden by Mom's Knife.
 * : Overridden by Mom's Knife.
 * : Damage is doubled and no damage decrease with distance.
 * : Overridden by Mom's Knife.
 * : Overridden by Mom's Knife.
 * : Overridden by Mom's Knife.
 * : Damage drastically reduced at the benefit of a slightly better fire rate.
 * : Overridden by Mom's Knife.
 * Both the knife and the laser fire normally.
 * : 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.
 * : When Isaac changes direction, the knife snaps into the direction Isaac is facing.
 * : Overridden by Mom's Knife.

Trivia

 * This item is used in Challenge #26 (I RULE!).
 * In the original Binding of Isaac, buying the item from the Devil Room cost 1 heart container instead of 2.
 * The description of the item is a possible reference to the sniper's dialogue in Team Fortress 2.

Seeds
8CKM J108 (Treasure room adjacent to spawn) 6PG9 7RK3 (Treasure room up and to the right one room from spawn) DVNV YV9Y (Treasure room adjacent to spawn) JW43 H8EK (Treasure room adjacent to spawn) 1M9E Y1G1 (Treasure room adjacent to spawn) P8SE A9JW (Treasure room adjacent to spawn) S63T 434W (Treasure room adjacent to spawn) JZCL 97JE (First Golden Treasure Room)