Who would you say is the "Flygon" of each gen?

In other words, popular or fan favorite mon who have still yet to receive any new form like a mega, regional variant, paradox, g-max, etc because either the devs actively hate them, or always have artist's block with them.

I know it's weird I put gen 9 mons here, but I placed them here for the possibility of them joining this group of Pokemon cause I can see them being neglected for a new form for a long time while a ton of other mons from the same gen as them receive a form