I’ve wasted too many hours on Shatter Pixel Dungeon.
You can get the source for OG Pixel Dungeon off GitHub, but there’s a maintened version on the F-Droid store (Shatter Pixel Dungeon). There’s some other free versions floating around too, not sure if they’re on the F-Droid store too, but I know they’re on the play store.
Haven’t played Origins, but I’ve spent a lot of time with Odyssey which has my highest recommendation.
From a friend who’s opinion I trust, I’ve been told Origins is the less fleshed out version of Odyssey. He says that Origins started Assassin’s Creed on a new RPG focused track that really just worked for Origins and Odyssey (he claims they biffed Valhalla).