Pokécharms

You mean similar to that of an Ultra Beast or an "Epically failed experiment" or do you mean like a creature from Lovecraft?

I’d mean a Lovecraftian-esque beast — or perhaps like Ulamog/Emrakul of Magic: The Gathering, though mostly the latter two, since that would be where I’m basing a piece of lore from.

In specific, the idea of a powerful beast from outside the realm that sends ‘emissaries’ or ‘avatars’ down to a specific region — would such an avatar count as a Pokémon? And if so, would they classify as a legendary, or would they be more common?

If it helps, I’m doing this in the context of a ‘what-if’ where Gen 1’s many glitch pokemon actually were real Pokémon in Kanto lol

Hypothetically you could make a eldritch abomination inspired pokémon. I'd say it would be dark/psychic. Dark because its lovecraft. psychic because its reality warping abilities.