Increase the shiny odds of wild or static encounters while also giving red gyarados more random DV spreads. - pret/pokecrystal GitHub Wiki
Ever wanted to change the shiny odds in your project without changing how the game determines that a Pokemon is shiny? well read more below to learn how to do it for yourself.
located in /engine/battle/core.asm
Once opened you want to look for the function .NotRoaming: (around line 6109)
.NotRoaming:
cp BATTLETYPE_FORCESHINY
jr nz, .TryShinyRolls
jp .AlwaysShiny ; Forced Shiny Encounter
.TryShinyRolls:
; Try to roll for a shiny encounter
call Random ; 8-bit random -> a
ld b, a
call Random ; 8-bit random -> a
ld c, a
; Combine into 16-bit: b = high, c = low
; Reduce to 0–4095
ld a, b
and $0F ; low nibble 0–15
ld h, a
ld l, c
; Only jump to AlwaysShiny if exactly 4095
ld a, h
cp 15
jr nz, .NormalDVs
ld a, l
cp 255
jr nz, .NormalDVs
jp .AlwaysShiny
.AlwaysShiny:
; --- Pick a random valid shiny DV combination ---
call Random
and %00000111 ; pick 0–7
ld e, a ; save choice
; Map choice to valid shiny Attack DV
ld a, e
cp 0
jr z, .S0
cp 1
jr z, .S1
cp 2
jr z, .S2
cp 3
jr z, .S3
cp 4
jr z, .S4
cp 5
jr z, .S5
cp 6
jr z, .S6
; else combo 7
jp .S7
.S7:
ld b, $FA
ld c, $AA
jp .UpdateDVs
.S6:
ld b, $EA
ld c, $AA
jp .UpdateDVs
.S5:
ld b, $BA
ld c, $AA
jp .UpdateDVs
.S4:
ld b, $AA
ld c, $AA
jp .UpdateDVs
.S3:
ld b, $7A
ld c, $AA
jp .UpdateDVs
.S2:
ld b, $6A
ld c, $AA
jp .UpdateDVs
.S1:
ld b, $3A
ld c, $AA
jp .UpdateDVs
.S0:
ld b, $2A
ld c, $AA
jp .UpdateDVs
.NormalDVs:
; --- Normal random DV generation ---
call BattleRandom
ld b, a
call BattleRandom
ld c, a
; hl points to Pokémon DVs in memory
ld a, [hl] ; Attack/Defense DV byte
ld b, a
and $F0 ; high nibble = Attack
srl a
srl a
and %00000011 ; Attack DV mod 4 -> a
cp $02 ; compare with 2
jr z, .CheckShinyDefense
cp $03
jr z, .CheckShinyDefense
; Not shiny
jr .NotShiny
.CheckShinyDefense:
ld a, [hl] ; Attack/Defense DV byte
and $0F ; low nibble = Defense
cp $0A
jr nz, .NotShiny
inc hl ; move to next byte (Speed/Special)
ld a, [hl] ; Speed/Special DV byte
and $F0 ; high nibble = Speed
cp $A0 ; compare with 10 << 4
jr nz, .NotShiny
ld a, [hl]
and $0F ; low nibble = Special
cp $0A
jr nz, .NotShiny
; If reached here, Pokémon is shiny
jr .NormalDVs
.NotShiny:
; normal handlingAnd that's it. This also ensures that the red gyarados or other forced shiny encounters are given a random shiny attack dv so that there is some randomness involved.
Changing the shiny odds is fairly simple.
You want to find the .TryShinyRolls: function from our code and look for where it says cp 255, all you have to do is lower this value from 0-255 and your odds of getting a shiny encounter will increase.
