Formes like shadows and gold? He just answered it...
Go in PokemonUtilities, look for def pbLoadPokemonBitmapSpecies(pokemon, species, back=false)
in it, there is
bitmapFileName=sprintf("Graphics/Battlers/%03d%s%s.png",species,
pokemon.isShiny? ? "s" : "",
back ? "b" : "")
If...