A drop of urine, with light reflecting in it.
Makes Isaac appear happy and smiling while yellow colored projectiles (urine) come from his lower body rather than his face.
- Any Range stat increasing items (Mom's Underwear for example), will help you regain range lost from picking up Number One.
- If you have Number One and you have not yet entered The Womb, all Range Down Pills will be converted into Range Up Pills. Note that they do become Range Down again once you enter The Womb.
- Cancer - Breaks the default Rate Of Fire cap, giving Isaac a very high fire rate.
- Technology - Technology has infinite range, and thus Number one solely increases the fire rate.
- Brimstone - The charge time of the beam is decreased, with no real downside, since the beam has infinite range.
- Mom's Knife - Stacks.
- Dr. Fetus - Stacks.
- IPECAC - Stacks. The decreased range can be considered a plus, as it makes IPECAC shots easier to aim, while still having enough range to not hit Isaac.
- The Mulligan - The high fire rate allows the player to spawn many more Attack Flies.
- Tough Love - The high fire rate allows the player to spawn many more teeth.
- "Number one" is an informal term for urination, often used when speaking with children.