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Game

Pokémon Crystal

A Generation II Pokémon game for Game Boy Color, read through the pret/pokecrystal disassembly.

draftAlso: Pokémon Crystal VersionUpdated 2026-10-20
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Pokémon Crystal is a Generation II game for the Game Boy Color, released in Japan in December 2000 and North America in July 20011. The code read here is pret’s pokecrystal disassembly.

In type effectiveness, Crystal adds Steel and Dark2 and changes four older matchups3. Immunity becomes an explicit miss4, and Foresight removes the Ghost immunities5.

Interactive: type-matrix (needs JavaScript)

Crystal’s type chart. Cells changed since Red/Blue are outlined.

Uses

Linked from

Every claim about this game, by concept (19)
generalPokémon Crystal (developer Game Freak, publisher Nintendo, Game Boy Color, and Generation II core series) came out in Japan on 14 December 2000 and North America on 30 July 2001.T1
Damage formulaType still picks the stats: Steel is physical (below SPECIAL); Dark is special, using Special Attack against Special Defense.T3
A plain damaging move runs critical, damagestats, damagecalc (base formula, item boosts, and critical ×2), stab (weather, badges, STAB, and type rows), damagevariation, and then checkhit (accuracy).T3
The random factor is unchanged from Red/Blue, a random byte from 217 to 255 over 255.T3
Same-type attack bonusBattleCommand_Stab applies weather and badge type boosts, then STAB (damage+⌊damage/2⌋ if either attacker type matches), then the type chart.T3
A comment in pokecrystal's BattleCommand_Stab expands STAB as “Same Type Attack Bonus”.T3
Type effectivenessCrystal's type chart (TypeMatchups) has 108 non-neutral rows over 17 types, then a -2 marker, Normal→Ghost and Fighting→Ghost ×0, and a -1 end.T3
Multipliers are unchanged from Red/Blue: scaled by 10, with SUPER_EFFECTIVE 20, NOT_VERY_EFFECTIVE 05, NO_EFFECT 00, and EFFECTIVE 10.T3
Crystal's type constants add STEEL (physical), DARK (special), and an unused CURSE_TYPE named “???”; BIRD remains, still with no rows.T3
Struggle returns from BattleCommand_Stab at once, so it skips weather, badge boosts, STAB, and the type chart.T3
Each matching row computes damage×value; a nonzero product becomes ⌊product/10⌋, raised to 1 if that truncates to 0.T3
A ×0 row now marks the attack as missed outright, instead of relying on the damage reaching 0.T3
A ×¼ hit no longer truncates to a miss: 2 damage through two ½ rows gives ⌊2 × 5 / 10⌋ = 1, then ⌊1 × 5 / 10⌋ = 0, raised to 1.T4
Against an identified (Foresight) target, the loop stops at the -2 marker, skipping the Normal→Ghost and Fighting→Ghost immunities after it.T3
After the loop, CheckTypeMatchup's combined value (m=⌊m×row/10⌋ from 10) replaces the effectiveness byte, so the text reflects every row: ×4 is 40, ×¼ is 2, and ½ with 2× is 10.T3
An Ice move against Water/Flying (½ at L35, 2× at L39) prints no effectiveness text: the combined value goes 10 → 5 → 10.T4
Row order still matters: an Ice move against Water/Flying takes 3 damage to 1, then 2 (½ row at L35, 2× at L39).T4
Crystal's type chart makes Ghost-type moves super effective on Psychic types.T3
Crystal's table adds Steel and Dark and changes four Red/Blue matchups: Poison→Bug ×2 → ×1, Bug→Poison ×2 → ×½, Ghost→Psychic ×0 → ×2, and Ice→Fire ×1 → ×½.T4

References

  1. ^Pokémon Crystal (developer Game Freak, publisher Nintendo, Game Boy Color, and Generation II core series) came out in Japan on 14 December 2000 and North America on 30 July 2001. T1Bulbapedia, “Pokémon Crystal Version” · infobox, Basic info and Release dates
  2. ^Crystal's type constants add STEEL (physical), DARK (special), and an unused CURSE_TYPE named “???”; BIRD remains, still with no rows. T3pret/pokecrystal · constants/type_constants.asm L9–37, data/types/names.asm L37probe probes/pokemon-types/type-charts.mjs
  3. ^Crystal's table adds Steel and Dark and changes four Red/Blue matchups: Poison→Bug ×2 → ×1, Bug→Poison ×2 → ×½, Ghost→Psychic ×0 → ×2, and Ice→Fire ×1 → ×½. T4pret/pokered · data/types/type_matchups.asm L1–85pret/pokecrystal · data/types/type_matchups.asm L1–118Bulbapedia, “Type/Type chart” · Changes: Between Generations I and IIprobe probes/pokemon-types/type-charts.mjs
  4. ^A ×0 row now marks the attack as missed outright, instead of relying on the damage reaching 0. T3pret/pokecrystal · engine/battle/effect_commands.asm L1329–1336
  5. ^Against an identified (Foresight) target, the loop stops at the -2 marker, skipping the Normal→Ghost and Fighting→Ghost immunities after it. T3pret/pokecrystal · engine/battle/effect_commands.asm L1302–1310, data/types/type_matchups.asm L112–116

Sources

Code

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