I guess it comes as no surprise that everybody who plays an instrument in fact plays several, Level42 Bassplayer Mark King is known for his slapping bass style but he's also a killer on drums and no slough on guitar either. Flea of the Red Hot Chili Peppers is a mean bassplayer but he's also a clasically trained trumpet player who once was heralded as the next Herb Albert, Ray Charles is a well known keyboardist but he was also a saxophone player.
So with that in mind, some bands like to show off what else they can do by switching roles on stage, I figure it to be fun to show those instances when a switcheroo was performed.
First up, here's Metallica performing Diamond Head's "Am I evil" with leadsinger James Hetfield drumming, Bassplayer Jason Newsted playing lead guitar, guitarist Kirk Hammet playing bass and Drummer Lars Ulrich singing.
And here's Pantera performing Metallica's "Whiplash" with Leadsing Phil Anselmo playing guitar and guitarist Dimebag Darrel singing. Note also that they have Jason Newsted as guest bassplayer here.
Here's Nirvana playing "Seasons in the sun" with leadsinger/guitarist Kurt Cobain playing drums, Drummer Dave Grohl playing bass and Bassplayer Krist Novoselic playing (an out of tune) guitar.