The act of having a fainted Pokemon use the move, Surf, outside of battle to ride across bodies of water, even though it is not able to be used in battle.
Guy #1: SHIT!!! How am I going to get across the Whirl Islands now?
Guy #2: Dude, just use Surf
Guy #1: I can't Poliwag fainted.
Guy #2: You could always Corpse Surf.
Guy #1: Oh Yeahhhh