Fearow
Arbok I thought this was Corbeau's ace before playing Z-A.
Nidoking Giovanni's ace...there's a hypothetical remake of the originals where this makes a debut.
Nidoqueen
Venemoth For whatever it's worth, it did get a nice feature in the final dungeon of Scarlet and Violet.
Parasect I'm a fan, but there is neither a design nor competitive reason to give an alternate form; there's not much improvement to be had here.
Golduck
Dewgong There's no saving this design or Hypno's.
Hypno
Dodrio
Seaking desperately needs it
Ditto like Mew, doesn't need it conceptually
Omastar There's a lot of potential with fossils. No doubt they have power-ups and forms lost to time. If a special form was time-limited in battle only like Terastal, Mega, or Dynamax, it wouldn't appear in the fossil record.
Kabutops
Mew