In this game you can play as Mario Classic and New, Luigi Classic and New, Sonic, Tails, Samus, Vile, Zero, Proto man, Roll and a bunch of others, and it's still in the Beta.
Each character has power ups similar to the Mario ones. The mushrooms and fire flower types. A lot of the form shifting power ups do some interesting things. Like Tails can become Gyro man, or Luigi can become Proto man, etc. Check it out.
I love this game so hard. Plus, it's a download, so if you're offline you can still play it.
Here's the forum
http://s4.zetaboards.com/mkfusion/index/Here's the wiki
http://mkfusion.wikia.com/Here's the game
http://www.sendspace.com/file/vde5byHere's the latest patch
http://www.sendspace.com/file/9rg5p0TO INSTALL: Dump the content of this zip into you MKF 0.4 folder. If you did it right you should be told a number of files are being overwritten.