That makes for me 1 option left: Zygarde.
A legendairy Pokemon (no mythical) with more then 2 forms (no Mega/Primal)? Honestly Zygarde is the only one I know that fits this. All the others with multiple forms are Mythical.
EDIT: Oh, forgot about Necrozma! But that wasn’t the solution neither.
Wouldn’t know either, unless Deoxys counts as legendary, but it isn’t.
Silvally? It can change type, but I believe his form stays the same.
Correct, its Silvally
I have the perfect Halloween move!
Gourgeist that was easy
Make another one
I have multiple formes.
(Don’t even remember which one I had in mind back then).
Darmanitan-G Zen Mode?
I believe in the main series Ash allready saw a Ho-Oh before Charizard came in the picture. Next to that Moltres is also gen 1 and the same typing.
Hint? There’s like hundreds of different type combinations