>>713441432
There's a NSFW PMD fangame where you start a dungeon at a set level and there's effects that can lower it, and I think at least one modifier that can keep making it go down. The MC is a Lucario (surprise) and at a given point they devolve into a Riolu. Weird since it evolves via friendship, but whatever.

Though, surely there's at least some proper games where losing or exchanging hard-learned levels isn't that uncommon.