Triple battle. Granbull that knows Mimic. Smeargle that knows Sketch. Darkrai that knows Dark Void. 1st turn, Darkrai uses Dark Void, Smeargle uses Sketch, then Granbull uses Mimic on Smeargle thus aquiring Sketch for the battle. 2nd turn, Darkrai uses Dark Void, Smeargle does something, Granbull Sketches Dark Void! Would Granbull keep Dark void after the battle? Would it break the game? Would it be banned from wi-fi as a glitch? Will it change the world?
Dark Void is an example hypothetically it would work with any move.