XSp.

I read this confusing post few days ago about how Super Mario Bros level 1 would look if ported to the SNES. But the level looked like a mix of Super Mario Bros 2, with Super Mario Bros 3 elements, and some stuff I never saw before.

So I decided to research a bit more about it, and thus I came to know about Mushroom Kingdom Fusion, a fan made game with modified Mario gameplay with other games cross over elements.

Here’s the video I mentioned up there.
Super Mario Land 1 / Super Mario Bros. 1 remake:

Here’s Link from Legend of Zelda on Mushroom Kingdom Fusion:

Interesting eh? Notice each character has it’s own weapons and characteristics… like health system and stuff.

And then, Arthur from Ghouls and Ghosts series:

Ok, you thought that was awesome? Look at this one then:
Metal Slug level in Mushroom Kingdom Fusion

Well, if you’re still not impressed, **** you. 😛
Sorry about that… if you’re still not impressed you are probably not old enough… this game is clearly a tribute to several awesome old school games.

And even some new… here are some more videos:
Metal Sonic in Mushroom Kingdom Fusion

Contra in Mushroom Kingdom Fusion

Super Mario Fusion (old name) – Mario Meets Halo

Super Mario Fusion (old name) – Mario Meets Megaman

Some info now: Though lots of people seem to be part of the project, seems the main guy behind all this is JudgeSpear, also the author of most of the videos. Full credit list, platforms used, and other stuff at the wikia entry.
As I was writing this post, the latest version of the game was at demo v0.3. If you want to check it out, click the image at the beginning of the post or this link to a Wikia entry on the game, which will probably have the latest version released so far.

Source: TechEBlog and TechEBlog