Pokémon species data structure (Generation III)

Specs

A base stats structure is a 28-byte piece of data

Every Pokémon species in the Generation III games has a 28-byte base stats structure stored in the game's ROM somewhere. It determines all information inherent to the species, such as base Sp. Defense, Types, Egg Groups, and EV yield.

Base Stats	Data whose names are marked with an asterisk (*) have more information below the table.
Name	Type	Description
Base HP	byte	The base HP used in calculating Pokémon of the species's HP.
Base Attack	byte	The base Attack used in calculating a Pokémon of the species's Attack.
Base Defense	byte	The base Defense used in calculating a Pokémon of the species's Defense.
Base Speed	byte	The base Speed used in calculating a Pokémon of the species's Speed.
Base Sp. Attack	byte	The base Sp. Attack used in calculating a Pokémon of the species's Sp. Attack.
Base Sp. Defense	byte	The base Sp. Defense used in calculating a Pokémon of the species's Sp. Defense.
Type 1*	byte	The first type of Pokémon of the species.
Type 2*	byte	The second type of Pokémon of the species.
Catch rate	byte	The catch rate used in calculating the probability that a wild Pokémon of the species will be caught.
Base Exp. yield	byte	The base Experience yield used in calculating how many Exp. points Pokémon who defeat another Pokémon of the species receives.
Effort yield*	word	How many EVs Pokémon who defeat another Pokémon of the species receives, and in what stats.
Item 1*	word	An item wild Pokémon of the species may hold.
Item 2*	word	Another item wild Pokémon of the species may hold.
Gender	byte	The value that is compared against the personality value of Pokémon of the species when determining what gender they will be, i.e. represents rate of females vs. males of the species.
Steps to hatch	byte	The cumulative number of steps that must be taken before an Egg of the species hatches, divided by 256.
Base Happiness	byte	The happiness/tameness at which Pokémon of the species have when first caught.
Level-up type	byte	The pattern of Experience which Pokémon of the species require to level up.
Egg group 1*	byte	Indicates an Egg Group that the species belongs to.
Egg group 2*	byte	Indicates another Egg Group that the species belongs to.
Ability 1	byte	Indicates a special ability that Pokémon of the species may have.
Ability 2	byte	Indicates another special ability that Pokémon of the species may have.
Safari Zone Rate	byte	Determines rate at which Pokémon of the species flee when encountered in the Safari Zone. Only Pokémon that appear in the Safari Zone have this set.
Color*	byte	The Pokémon's color.
0000	word	Padding.

Notes

Types

Types are enumerated like this:

00. Normal	01. Fighting	02. Flying	03. Poison	04. Ground	05. Rock
06. Bug	07. Ghost	08. Steel	09. ???	10. Fire	11. Water
12. Grass	13. Electric	14. Psychic	15. Ice	16. Dragon	17. Dark

Type 9 (???) can be an actual type for a species as well as a type for an attack.

Effort yield

Certain bits count for particular stats:

(MSB)                    (LSB)
 0000  11  11  11  11  11  11
empty SDF SAK SPD DEF ATK  HP

Items

Items in the first "slot" have a 50% probability of being on the Pokémon, while 5% in the second "slot". If it's the same item in both then it's up to 100%.

Gender

Gender is zero for always-male Pokémon, 254 for always-female Pokémon and 255 for gender-neutral. Everything inbetween is a percentage value: Pikachu, 50% chance of being female, has 127.

Egg Groups

This determines with which type of Pokémon the Pokémon can breed to get eggs. See Egg groups. These are the direct values of the groups:

01. Monster	02. Water 1	04. Bug	05. Flying	06. Ground
07. Fairy	08. Plant	09. Humanshape	10. Water 3	11. Mineral
12. Indeterminate	13. Water 2	14. Ditto	15. Dragon	16. No Egg

Colors

Colors don't really affect any part of the game mechanics; though the MSB bit is set on some pokémon. Here is the list of the values and their relating colors:

00. Red	01. Blue	02. Yellow	04. Green	05. Black
06. Brown	07. Purple	08. Gray	09. White	10. Pink

Storage

The following are ROM offsets for the first entry (Bulbasaur) in each GBA game (US version?):

• Ruby: 0x001fec34
• Sapphire: 0x001febc4
• Emerald: 0x002f0d70
• FireRed: 0x002111A8
• LeafGreen: 0x00211184
• LeafGreen (EN-US): 0x0025477C