Certainly one of the better Super Mario Bros. hacks—actually a Game Maker 7 Pro creation—we've ever seen, Super Mario Fusion sees the portly plumber take part in a two-dimensional, Covanent killing adventure. Cherry-picking gameplay and graphics from the Super Mario All-Stars version of Super Mario Bros. 2 and Super Mario World, then tossing in some aliens who are easily dispatched by laser or turnip, then topping it off with a Halo soundtrack works better than one might think. Killing Buzzy Beetles and Grunts just feels right, at this point.
If you're still interested after 12 minutes of demo video, pop on over to the YouTube page on the matter for the playable public beta.
Super Mario Fusion [YouTube - thanks, Mae!]