All of the homonculi, several characters, including the possessed doll, Red.
This was unintentionally done by Easan the Mad the Darklord of Vechor in the Ravenloft campaign setting. The citizens of Vechor worship him as a god, despite the fact that this is one of the few things he has never actually claimed. (Although he hasn't denied it either, and he certainly does have powers that seem godlike to them.) Oddly enough, they also know that he's completely insane, although worshipping a mad god doesn't seem to be a problem to them.
New Dawn RP-Verse has a lot of these guys and gals:
Cruelly treated, misguided Sarina, who wanted to become a Goddess so she can change things to...make herself good rather than evil, or something.
Manipulative, hidden agenda executing Ignius, who reigns supreme over an entire dimension, and actually has a relatively solid claim to the title.
Demonic Conqueror Mihra, who styles himself a God, and possesses a shadowy, devouring force that might be cosmic entropy.
We Are All Pokémon Trainers has Eon, who being a Latios is part of a species that are considered deities IRP, but he appears to have delusions of being on the same tier of power as legends like Groudon and Dialga.