Old gods

When any god, less than Elder status, loses all of their followers and is forgotten, their divinity and godhood goes with it. This causes their bodies to decay into a hideous monstrosity physically. When a god loses their godhood, no matter how many new followers they gain back, they will never be able to regain their divine strength and their name being lost in the past forever.
There are small people groups that worship the old gods after they have become an old god. Several wild tribes, witch covens, and cults pay homage to them and some even call upon them as a patron for warlock pacts.
When a god becomes an old god, not all power is striped from them. They still maintain immense power of whatever they were a god of from before. They just lose their divine right and god status. Forever banished from the heavenly realm of Serenios. There are some old gods whose pure power alone can rival that of a god.
If you choose to worship an old god you might get a more intimate experience with them than with a traditional active god of one of the many pantheons. Old gods cannot acend to the celestial plane of Serenios like before and are forced to walk among the mortals in the material plane of Baltharos.