Somebody combined Mountain Song and Smashing Pumpkins Cherub Rock.
At first I was grimacing, but then it sorta started clicking.
Cherub Mountain
http://www.youtube.com/watch?v=hoUhXJJpAag
They do it twice, first with Perry singing on top of Cherub Rock (works pretty well, actually), then Billy singing on top of Mountain Song (this one sounds like shit, to me anyway).
But it's worth a watch. Pretty bizarre.