The best game randomizer mods and modes on PC

Games are great aren't they? They throw you into vast worlds where you can save everyone from monsters and explore strange new lands. But what do you do when you've finished your game? You could just download a mod to add new things or change the game completely, and that's fine. But how about randomizing the stuff that's already in the game, like items, enemies, skills, and where you expect to find them.
Game randomizer mods are more of a recent trend, and one that's far more common with retro console or handheld games (Pokémon is probably the best known candidate for randomizer mods), but there are plenty of game randomizer mods for PC. Randomizer mods do skew somewhat towards RPGs, since changing enemy and item placement is a common theme among them, but very occasionally something a lot more unorthodox will appear from out of nowhere.
If you do wish to explore this weird, wonderful universe of randomizers, I should point out some caveats. A lot of the randomizers out there are mods that are found on Nexus Mods - which is a fairly reputable source for mods for all sorts of games, but there are also more than a few that are just uploaded to GitHub. There is very little regulation on GitHub, so they could contain malicious software. Make sure your virus protection is enabled before downloading ones from there.
RELATED LINKS:
Bloodstained sells 1 million units, gets four more free DLC updates this year
Bloodstained: Ritual of the Night reviews on Steam are incredibly positive
Bloodstained: Ritual of the Night is out in June, and it doesn't look like "poop" anymore