Number One

Treasure Room Treasure Room   (page 1, column 6, line 1) (page 1, column 6, line 1)

Number One is a passive item.

Effects

• +1.5 tears.
• -17.62 range.
• +0.76 tear height.
• Tears turn yellow and are fired from Isaac's lower body rather than his head.

Interactions

• Azazel: Lowers range, reduces charge time.
• Compound FractureIncreases range. Tears turn into bones, which shatter into 1-3 bone shards upon hitting an enemy or obstacle./ The ParasiteIsaac's tears split in two when they hit something.: Tears often disappear before being able to split. Split tears also only travel a very short distance.
• Cricket's BodyGrants -1 Tear Delay and reduces Range. When tears hit an object or deplete their range, they spawn 4 smaller tears, whose Range and Damage scale with Isaac's.: Tears disappear very quickly after being fired and split tears barely travel at all.
• Dr. FetusTears are replaced by bombs that benefit from bomb-enhancing effects and slide a fixed range after being fired.: Not recommended. Bombs do not travel far, making self damage very likely.
• HaemolacriaTears are now fired in an arc. Upon hitting the floor, an obstacle, or an enemy, they burst into many smaller tears in all directions. Increases tear delay.: Does not affect main tear; however, burst tears travel significantly less far.
• Kidney StoneRandomly while firing tears, Isaac will stop firing and turn red, where he will charge and release a lot of 'tears' in one go. In the burst of tears is a kidney stone which deals a lot of damage.: Tear barrage fires a very short distance before disappearing. Does not affect the stone.
• A Lump of CoalThe more distance tears travel, the more damage they will do.: Tears still increase in size and damage as they travel; however, the short range limits tear size and damage.
• MarkedIsaac will now fire tears automatically directed at a red target on the ground which is controlled by the player. This allows for a full 360 degree tear firing radius. Can be overridden by other tear modifiers such as Mom's Knife or Brimstone.: Tears become orange. Firing rate is increased, Marked's effect is unaffected but range is reduced.
• Mom's KnifeIsaac's tears are replaced by a knife that pierces enemies, can travel through obstacles, and can hurt enemies while Isaac is holding it. Holding down the fire button before firing increases its range and power.: The knife turns yellow and the maximum range is significantly reduced.
• Monstro's LungIncreases damage and grants a charged shot that fires multiple tears in the same fashion as Monstro./ Lead PencilAfter every 15 tears fired, Isaac will fire a high-damage cluster of tears.: Not recommended. Tear barrage disappears very close to Isaac.
• ProptosisTears start out massive with high damage, and then shrink down and become weaker over a short range.: Not recommended. Tears disappear after traveling a very short distance.
• Rubber CementTears bounce off walls, enemies, and environmental objects.: Tears often disappear before being able to bounce off walls.
• Toothpicks+0.7 tears, +16% shot speed.: Tears become orange.

Synergies

• BrimstoneTears are replaced by a laser beam that pierces through all enemies and obstacles in its path and deals high damage. Can only be fired after a short charge-up period.: The laser turns yellow and charges at a much faster rate with no decrease to range.
• Epic FetusIsaac's tears are replaced with guided missiles, like those used by the Doctor's Remote.: Increases firerate with no decrease in range. Explosive clouds are now yellow.
• IncubusA demonic familiar that follows Isaac and shoots tears identical to Isaac's in terms of damage, range, fire rate, and effects.: The Incubus fires at a much faster rate with no decrease to range.
• IpecacReplaces tears with explosive and poisoning projectiles fired in an arc from the mouth.: Increase fire rate moderately and decreases range only slightly.
• The Ludovico TechniqueInstead of firing tears, Isaac controls one floating tear that hover over obstacles. This tear deals constant damage when held in place over an enemy.: Turns tear yellow and allows it to be moved much faster.
• Pop!Replaces Isaac's tears with eyeballs that can bounce off of each other. The eyeballs are not limited by range, and will instead dissipate when they stop moving or when hitting an enemy or obstacle.: Eyeball tears are yellow, can be fired much quicker, and does not affect their airtime.
• TechnologyReplaces tears with a piercing laser with unlimited range.: The laser turns yellow and Technology's firing rate is greatly increased with no decrease to range.
• Tech XTears are replaced with laser rings that pierce through enemies and deal damage to enemies within them. Can be charged to increase the size of the ring.: Laser turns yellow, charge time is greatly decreased, and no decrease to range.
• Tiny PlanetRange up and makes shot tears revolve around Isaac until they drop.: Tears travel roughly the same distance but can be fired much quicker.

Trivia

• "Number One" is a euphemism for urination.
• In the original Binding of Isaac, Number One had the effect of turning all future Range Down pills into Range Up pills. This was presumably designed to reduce the risk of players being stuck in situations where their range would become too low to clear certain rooms. However, in Rebirth, Number One no longer has this effect, and will not turn Range Down pills into Range Up pills.
• This item is used in Challenge #2 (High Brow).
• The firing animation of Number One is a little different from what it looks like in the original Binding of Isaac.

Seeds

 PC  J172 PRAK (Treasure room adjacent to spawn)

 PC  VMA3 SMZA (Treasure room adjacent to spawn)

 PC  SRX8 FXHM (Treasure room adjacent to spawn) (XL floor) (Hard mode only)

 3DS  0RJ7 VQYY (First floor treasure room)

 PS4  WYH4 A4DX (First floor treasure room)