>>53510187>>53510747>>53512220>>53512326Melmetal is labeled in all canonical media as not being from any generation or region. You could definitely argue that Melmetal is a gen 8 Pokémon due to it having a gigantimax form, but that comes into conflict with the fact that it's in LGPE, a gen 7 game. It seems like Game Freak would rather exclude it from the conventional definition of generations since it's closers to a side-game Pokémon than any other Pokémon that came before it, since it effectively originates from Pokémon GO.
