So here's every realizable, relevant Pokémon that could conceivably get a slot in Smash Ultimate; that isn't already deconfirmed. Some are much more likely than others, but they all have a chance to get in (not accounting for an Alfonzo situation, which would throw in Pokéball/stage hazard mons into the mix).
>Machamp
>Gengar
>Heracross
>Grovyle
>Sceptile
>Gardevoir
>Torterra
>Lopunny
>Weavile
>Dusknoir
>Genesect
>Sylveon
>Hawlucha
>Decidueye
>Incineroar
>Lycanroc-Dusk
>Lycanroc-Midnight
>Golisopod
>Kommo-o
>Silvally
>Tapu Koko
>Buzzwole
>Necrozma
>Zeraora
Any questions?