Pokémon species data structure (Generation II)

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Specs

A base stats structure is a 32-byte piece of data.

Every Pokémon species in the Generation II games has a 32-byte base stats structure stored in the game's ROM somewhere. It determines all information inherent to the species, such as base Defense, Types, catch rate and egg groups.

Offset Contents Size
0x00 Pokédex number byte
0x01 Base HP byte
0x02 Base Attack byte
0x03 Base Defense byte
0x04 Base Speed byte
0x05 Base Sp. Attack byte
0x06 Base Sp. Defense byte
0x07 Type 1 byte
0x08 Type 2 byte
0x09 Catch rate byte
0x0a Base Exp. Yield byte
0x0b Wild held item 1 byte
0x0c Wild held item 2 byte
0x0d Gender ratio byte
0x0e Unknown byte
0x0f Egg cycles byte
0x10 Unknown byte
0x11 Dimensions of front sprite byte
0x12-0x15 Blank 4 bytes
0x16 Growth rate byte
0x17 Egg groups byte
0x18-0x1f TM and HM flags 8 bytes

Notes

Types

For a single-typed 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

Wild Held Items

Sources disagree about the exact chance for each slot. UPC says 25% and 8%, Serebii says 25% and 1.5%.

Note that, unlike subsequent generation of games, if both item slots are set to the same item, the chance is not 100%.

Growth Rate

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

Blank

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.

Frontsprite dimensions

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

Egg Groups

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

TMs

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.

Fingerprint

Gold/Silver

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
...

Crystal

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
...

Storage

The following are ROM offsets for the first entry (Bulbasaur) in each GBC game:

  • Gold (en): 0x051b0b
  • Silver (en): 0x051b0b
  • Crystal (en): 0x051424


Data structure in the Pokémon games
General Character encoding
Generation I Pokémon species • Pokémon • Poké Mart • Character encoding (Stadium) • Save
Generation II Pokémon species • Pokémon • Trainer • Character encoding (Stadium • Korean) • Save
Generation III Pokémon species (Evolution • Pokédex • Type chart)
Pokémon (substructures) • Move • Contest • Contest move • Item
Trainer Tower • Battle Frontier • Character encoding (GameCube) • Save
Generation IV Pokémon species (Evolution • Learnsets)
Pokémon • Save • Character encoding (Wii)
Generation V–present Character encoding
Generation VIII Save
TCG GB and GB2 Character encoding
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