How to make a rotom change form event with tutorial

[Umbreon]

Alright here I'll show you my tutorial on rotom form changing

call with pbRotomForm1

# Start here
def pbRotomForm1 # Defines the call method
pkmn=pbFirstAblePokemon # get's the first pokemon that has 1hp+
if pkmn!=479 # checks if the pokemon is rotom.
Kernel.pbMessage(_INTL("Your text here if not rotom.")) # text if you don't have rotom first in your party.
return false # exits the script as false
end # ends the if branch
Kernel.pbMessage(_INTL("Your text here if pokemon = rotom.")) # text if you have rotom in the first slot with 1+ hp.
pkmn.form=x # (change form by replacing x 0 is normal 1+ is different forms, it is different for each kit.)
end # ends the script.
###End Script###


Well it's as simple as that!

[p.claydon]

just a quick question how does this choose the image for the different form is there a file name format that needs to be followed or something