Pokémon Ruby Version, Sapphire Version, and Emerald Version - Personality ID
Each Pokémon comes with an unsigned 32-bit integer ID, generated at random, which determines significant information about the uniqueness of the Pokémon. (This ID is sometimes called "Personality Value" or "Personality ID". It is not to be confused with a Pokémon’s Trainer ID.)
Ability
A Pokémon’s initial ability is determined by whether the personality ID is odd or even. If it’s even, it has the first ability, and if odd, the second ability.
Gender
The remainder of a Pokémon’s personality ID divided by 256 contains that Pokémon’s gender value. Each Pokémon species has one of the following seven gender rates.- 12.5% female - If gender value is 0 through 30, the Pokémon is female; otherwise, male.
- 25% female - If gender value is 0 through 63, the Pokémon is female; otherwise, male.
- 50% female - If gender value is 0 through 126, the Pokémon is female; otherwise, male.
- 75% female - If gender value is 0 through 190, the Pokémon is female; otherwise, male.
- Always male - Always male regardless of gender value.
- Always female - Always female regardless of gender value.
- Gender-unknown - Unknown gender, regardless of gender value.
Unown form
To find the Unown form, the game does the following:- Set Y to the personality ID.
- Set A to the remainder of Y divided by 4.
- Divide Y by 256 and round down.
- Set B to the remainder of Y divided by 4, then multiply B by 4.
- Divide Y by 256 and round down.
- Set C to the remainder of Y divided by 4, then multiply C by 16.
- Divide Y by 256 and round down.
- Set D to the remainder of Y divided by 4, then multiply D by 64.
- Set X to A plus B plus C plus D.
- Set X to the remainder of X divided by 28.
Wurmple
For a given Wurmple, if the remainder of the personality ID’s high 16 bits divided by 10 is less than 5, it will evolve into Silcoon; else Cascoon.