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
00:17 Elite & Grunt Battle
01:18 9-4 The Library
13:31 Space Pirate Battle #2
15:04 9-S2 Anciena Pyramid (Normal Exit, WALDO boss fight)
28:34 9-S3 Battle for Sera (Doc Robot placeholder boss fight)