Here's a bunch of remixed medley ideas that will take quite a while for me to finish, but it's worth it.
Mario RPG Final Boss Medley
https://www.youtube.com/playlist?list=PL6Y9N-wSgnKoD7GPCziubtVJsr4aQZHSO
Donkey Kong Country Final Boss Medley
https://www.youtube.com/playlist?list=PL6Y9N-wSgnKqkDogC9tSMPsSF4WNkqMLi
Super Smash Bros. Final Boss Medley
(Haven't made playlist yet)
Final Fantasy Final Boss Medley
(Haven't made the playlist yet since there's so many games to keep track of)
Mario RPG Final Dungeon Medley
https://www.youtube.com/playlist?list=PL6Y9N-wSgnKp2IWgbkowiEeRepmp6CDEJ