Another day, another delightful mod. Today's takes the world of Skyrim and turns it into Mario World, complete with lush, cartoony environments, Goombas, coins -- all that good stuff. While the mod is primarily 3D, there's even a sidescrolling platform portion to enjoy, too.
There are a few downsides that will pull you out of the experience, some, unfortunately: you can't stomp on Goombas to kill them, and shrooms don't make you bigger. Presumably you can get over that, though, especially with five worlds and a few hours of play at hand.
Wonderfully, the mod installs itself in such a way that you can access "Mario World" as a separate world outside of Tamriel, so it won't overrwrite anything or screw up your regular sessions.
Hit the source to grab it while you can -- it's entirely possible Nintendo won't be too happy about it and demand it be removed soon.