Credits:

Defa

How To

Insert these bytes into free space and note the offset:

C0 B5 06 4E 36 78 64 27 7E 43 05 48 80 19 05 4E 00 F0 0C F8 04 4E 30 80 C0 BD 00 00 C0 70 03 02 84 42 02 02 71 44 04 08 D0 70 03 02 30 47

Set var4 to party Pokémon index (special ChoosePartyMon sets the index in var4) Returns in varResult, 0 if not shiny or 1 if shiny

Use callasm <offset+1> as usual

Happy Hacking!