This is a screenshot I just took in Doom II. Crazy! The modder responsible for the aptly-named "Donkey Kong Country for GZDoom" is none other than DooMero, whom you might remember for his Resident Evil Doom mod.
This current project of his basically turns Doom into a Donkey Kong platformer, although only an unfinished demo version has been released so far.
Here's a video of the mod in action. It appears to be a full playthrough of the demo:
To play, all you need is a copy of GZDoom, the mod, and a WAD file from one of the official Doom engine games (Doom, Doom II, Strife, Heretic, Hexen etc.) The controls are surprisingly tricky, so if you have a look, prepare to be frustrated.