One of the most popular Pokemon romhacks you can play right now meshes the creature catcher with the roguelite genre. While PokeRogue recently hit a significant milestone with the release of fan game's ending sequence, though, the the project's creator is stepping away to refocus on faith, family, and their job.
PokeRogue is Pokemon as you know it, but with procedurally generated worlds, so the map and encounters change with each playthrough. You won't find the sort of permadeath popularised in roguelikes or Nuzlockes, but you'll need to keep on top of things like resource management as who knows how things will play out. It's garnered some serious popularity, particularly among Pokemon's streaming community, but that's not stopping its creator from stepping away from the project.
