Pokémon species data structure (Generation II)

For a single-type Pokémon, both types are set to the same value.

• 0x00: Normal
• 0x01: Fighting
• 0x02: Flying
• 0x03: Poison
• 0x04: Ground
• 0x05: Rock
• 0x06: Bird
• 0x07: Bug
• 0x08: Ghost
• 0x09: Steel
• 0x0a:-0x12: blank
• 0x13: ???
• 0x14: Fire
• 0x15: Water
• 0x16: Grass
• 0x17: Electric
• 0x18: Psychic
• 0x19: Ice
• 0x1a: Dragon
• 0x1b: Dark

Main article: List of Pokémon by wild held item (Generation II)

The item entries refer to items by their index number. The first item has a 23% chance of being held when the Pokémon is encountered in the wild, while the second has a 2% chance of being held. However, if a special flag is set for a given battle, the Pokémon will always be holding its first item; this is used for Snorlax, Lugia, and Ho-Oh (although Lugia never has a held item).

The gender ratio is expressed as a 1-byte threshold for the Pokémon to be male. The possible values are:

A Pokémon's gender is calculated based on this threshold value and the Pokémon's Attack IV, following a certain set of rules.

One nybble each for width and height in 8×8 pixel tiles. They always match and are always 5, 6, or 7 tiles.

In the GB games, this is where the Pokémon's Lv.1 moves were stored. In GSC, Lv.1 moves were moved in with the rest of the moves.

• 0. Medium Fast
• 3. Medium Slow
• 4. Fast
• 5. Slow

The low nybble is one group, and the high nybble is another. For a Pokémon in only one group, both are set to the same value.

• 0x01: Monster
• 0x02: Water 1
• 0x03: Bug
• 0x04: Flying
• 0x05: Ground
• 0x06: Fairy
• 0x07: Plant
• 0x08: Humanshape
• 0x09: Water 3
• 0x0a: Mineral
• 0x0b: Indeterminate
• 0x0c: Water 2
• 0x0d: Ditto
• 0x0e: Dragon
• 0x0f: No Eggs

The TMs which a Pokémon can learn are stored as a bunch of flags. Starting from the LSB of the first byte, and ending with the MSB of the last byte. The seven HMs are treated as TMs 51-57.

In Pokémon Crystal, 3 bits after the HMs are used to indicate the ability to be taught Flamethrower, Thunderbolt, and/or Ice Beam by the Move Tutor.

01 2D 31 31 2D 41 41 16 03 2D 40 00 00 1F 64 14 05 55 00 00 00 00 03 17 26 1E 3D C4 86 18 45 00  // BULBASAUR
02 3C 3E 3F 3C 50 50 16 03 2D 8D 00 00 1F 64 14 05 66 00 00 00 00 03 17 26 1E 3D C4 86 18 45 00  // IVYSAUR
03 50 52 53 50 64 64 16 03 2D D0 00 00 1F 64 14 05 77 00 00 00 00 03 17 36 5E 3D C4 86 18 45 00  // VENUSAUR
04 27 34 2B 41 3C 32 14 14 2D 41 00 00 1F 64 14 05 55 00 00 00 00 03 1E A7 16 D9 CC E6 98 25 00  // CHARMANDER
05 3A 40 3A 50 50 41 14 14 2D 8E 00 00 1F 64 14 05 66 00 00 00 00 03 1E A7 16 D9 CC E6 98 25 00  // CHARMELEON
06 4E 54 4E 64 6D 55 14 02 2D D1 00 00 1F 64 14 05 77 00 00 00 00 03 1E B7 56 D9 CE F6 D8 2D 00  // CHARIZARD
07 2C 30 41 2B 32 40 15 15 2D 42 00 00 1F 64 14 05 55 00 00 00 00 03 12 AF B2 5B CC 87 18 B0 01  // SQUIRTLE
08 3B 3F 50 3A 41 50 15 15 2D 8F 00 00 1F 64 14 05 66 00 00 00 00 03 12 AF B2 5B CC 87 18 B0 01  // WARTORTLE
09 4F 53 64 4E 55 69 15 15 2D D2 00 00 1F 64 14 05 77 00 00 00 00 03 12 BF F2 5B CE 87 18 B0 01  // BLASTOISE
0A 2D 1E 23 2D 14 14 07 07 FF 35 00 00 7F 64 0F 05 55 00 00 00 00 00 33 00 00 00 00 00 00 00 00  // CATERPIE
...

01 2D 31 31 2D 41 41 16 03 2D 40 00 00 1F 64 14 05 55 00 00 00 00 03 17 26 1E 3D C4 86 18 45 00  // BULBASAUR
02 3C 3E 3F 3C 50 50 16 03 2D 8D 00 00 1F 64 14 05 66 00 00 00 00 03 17 26 1E 3D C4 86 18 45 00  // IVYSAUR
03 50 52 53 50 64 64 16 03 2D D0 00 00 1F 64 14 05 77 00 00 00 00 03 17 36 5E 3D C4 86 18 45 00  // VENUSAUR
04 27 34 2B 41 3C 32 14 14 2D 41 00 00 1F 64 14 05 55 00 00 00 00 03 1E A7 16 D9 CC E6 98 25 02  // CHARMANDER
05 3A 40 3A 50 50 41 14 14 2D 8E 00 00 1F 64 14 05 66 00 00 00 00 03 1E A7 16 D9 CC E6 98 25 02  // CHARMELEON
06 4E 54 4E 64 6D 55 14 02 2D D1 00 00 1F 64 14 05 77 00 00 00 00 03 1E B7 56 D9 CE F6 D8 2D 02  // CHARIZARD
07 2C 30 41 2B 32 40 15 15 2D 42 00 00 1F 64 14 05 55 00 00 00 00 03 12 AF B2 5B CC 87 18 B0 09  // SQUIRTLE
08 3B 3F 50 3A 41 50 15 15 2D 8F 00 00 1F 64 14 05 66 00 00 00 00 03 12 AF B2 5B CC 87 18 B0 09  // WARTORTLE
09 4F 53 64 4E 55 69 15 15 2D D2 00 00 1F 64 14 05 77 00 00 00 00 03 12 BF F2 5B CE 87 18 B0 09  // BLASTOISE
0A 2D 1E 23 2D 14 14 07 07 FF 35 00 00 7F 64 0F 05 55 00 00 00 00 00 33 00 00 00 00 00 00 00 00  // CATERPIE
...