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
00:18 6-F2 Fortress of Doom (Helmethead boss fight)
25:31 6-F4 Fire Temple (Flare Dancer boss fight)
41:59 6-F3 Forest Temple (Meg boss fight)