ive tried pokemon stadium 2, paper mario, dobutsu no mori (animal forest), smash 64, mario kart 64, and super mario 64 for n64, and all run well, with a gfx issue here or there
as for psx, i tried FF7, Spyro, and Crash, and all 3 run well.
Sonic Mania works fine for me:
surprised you got Metal Sonic working in MK8D. Unless you didnt straight up just take the files, and actually ported them.