Talking about iffy cores..Cave Story is still broken, but apparently it's broken on a few systems so its not WiiU specific.
The Fuse Core is working now!
I wish the issue with the saving in PrBoom could be fixed :/
I've been waiting on doing a complete pistol-start UV run of both Doom and Doom 2, but the fact that the saving/loading is borked on PrBoom as a whole is just really bad.
It seems the specific culprit and code at fault has been pinned down, it's just a matter of someone interested in fixing it:
https://github.com/libretro/libretro-prboom/issues/140