Catch rate glitches (Generation II)

In Pokémon Gold, Silver and Crystal, a wild Pokémon's catch rate is not affected if it is burned, poisoned, or paralyzed, despite those conditions increasing catch rate in other generations and the code seeming to attempt to factor them in. Sleep and freeze still affect the catch rate as intended.

Explanation

The code for factoring status conditions into catch rate reads as follows:

       ld b, a
       ld a, [WildPokemonStatus]
       and SLP|FRZ
       ld c, 10
       jr nz, .done
       ; ld a, [wEnemyMonStatus] ; bugfix
       and a
       ld c, 5
       jr nz, .done
       ld c, 0
       .done

What the code does is set a value increasing catch rate (referred to as "a" in Bulbapedia's explanation, linked below) to 10 if the opponent is asleep or frozen, and do nothing otherwise. The next few lines are presumably intended to set the value to 5 if there is a different status condition present; however, since the value of register a is already WildPokemonStatus & (SLP|FRZ), the second jr nz, .done is never taken, and the value is set to 0 anyway.

Inserting the commented line would fix this glitch.

See also

• Bulbapedia's article on catch rate

Attriution

• IIMarckus for discovery and the corrected code, in addition to everyone who helped with pokegold and pokecrystal.