The June 14, 2008 version of Mushroom Kingdom Fusion or the mp3 pack: http://mkfusion.ipbfree.com/index.php?showtopic=905
This version includes Doom, but Wolfenstein 3D is still in progress.
The November 17, 2008 version of Mushroom Kingdom Fusion or the mp3 pack: http://mkfusion.ipbfree.com/index.php?showtopic=3392
I haven’t checked yet to see if this version has Wolfenstein 3D because I just found out about it today.
Or as time goes by, you can download whatever may be the most recent beta version here: http://mkfusion.wiki-site.com/index.php/Main_Page
There are over 100 videos of MKF on Youtube. It first was called Super Mario Fusion and had only one developer. Now as MKF, it has a team.
You can play as Mario, Luigi, Sonic, and Tails at least in the outdated MKF v0.2 Beta RC1. Luigi's fireball is unchanged from one of The Super Smash Bros games.
I think that in the final versions, you will be able to play as Wario, Arthur (from Super Ghouls and Ghosts), Mario, Link, Sonic, Luigi, Tails, Kirby, Samus Aran (from Metroid), and Roll (from Megaman Legends and Megaman 64).
The game is Mario vs. The Mushroom Kingdom, alternate Earth, Halo, Doom, Tetris, Mega Man's world, shoot-em-ups, Sonic's world, Nintendo, the giant robotic wasp from Mario Paint, the Grand Canyon, a skyscraper level, and some things that I'm going to save as surprises instead of mentioning.
It has elements from Super Mario All Stars, Super Mario World, Super Mario Land 1, and 2, The Japanese version of Super Mario Bros 2 (Doki Doki Panic: The Dream Machine), and other games.
At least in the outdated MKF v0.2 Beta RC1 (The June 14, 2008 version), there are some disadvantages or bugs to this version of the game. It takes about a minute to load up. If you go to any switch palace other than the yellow one, then the game will have an error. If you press Shift to jump several times in a row without pressing other keys, then you will get a message on the screen. Don't go to the minus world unless your game is saved because you will get stuck.
I know that at least in the June 14, 2008 version, if you go to the minus world and go to certain areas as if they were levels, then they are secret levels.