Recently I discovered that people have actually started working on Mushroom Kingdom Fusion again, after it was in hiatus for a long time. It used to be maybe my favourite fangame ever, combining all kinds of different franchises while still keeping the Super Mario Bros 3 / Super Mario World style gameplay.
The game still isn't finished but I'm surprised they're working on it at all.
Levels included in this video:
00:00 Intro
00:20 9-8 Diamondus
08:34 9-10 The Energy Zone (Robo Corpse boss fight)
17:10 Grunt & Elite Battle #2
17:59 9-6 Interstellar Assault (Bacterion boss fight)
35:04 9-9 Moon Fortress (Star Man boss fight)