Not only can you play as Master Hand thanks to this mod, you control it with your actual hand. The beauty of motion controls, folks.
Here's Chadtronic trying out something called the "GameWAVE Mod," which he uses in conjuction with a Leap Motion in order to control Master Hand using gestures:
"I control Master Hand by mapping hand gestures which then convert into key combinations that are mapped to the controls in [an emulator]," Chadtronic wrote on the video's description. "As you can see there is a small delay and lag between actions, but hey, I'm surprised I was able to do this at all frankly!"
Considering how neat the concept is, I don't mind the lag -- it's still cool to watch. Now I wish I could play Smash Bros. as the bosses!
EDIT: as some have pointed out, playing as Master Hand has been possible via cheats. I altered the headline to more accurately reflect what's novel about this mod.
Controlling Master Hand with Leap Motion and GameWAVE Mod (Super Smash Bros) [Chadtronic]