Four levels are showcased in this video with two of them being remade levels from Super Mario Land 2 (I liked that Mario game on the Game Boy). The last one is a throwback to the airship levels of Super Mario Bros. 3 as Sonic is the character used in this level (Yeah Sonic and Tails are in this game). Watch out for music from Super Mario Galaxy and Super Smash Bros. Brawl in this clip (good choices of songs from those games).
Next up is a new Mega Man inspired level which is the Cutman level from the first Mega Man game (and Powered Up - the music is from Powered Up). It definitely looks and plays like that Mega Man level with Mario in it. YouTube user StarsimsUniverse nails these levels perfectly and he is a big Mega Man fan as well. The other characters available in MKF can use the Mega Man power up (like Mega Man Mario) but in different versions.
Lastly, here is Corpse of the Behemoth, one of the hardest levels in the game so far with Tails being the character played. The ending of this clip is kind of funny, but I'm pretty sure it will be fixed for the next beta.
So far, Mushroom Kingdom Fusion is going along nicely with the levels shown so far. The next beta is going to have lots of content in with more characters and levels to mess with. Even with all that greatness already in this fan-made game, there's still more yet to be done like more Halo levels, Sega levels (A remade Green Hill Zone level is in the works), and other stuff.