That, but you'll only see it in Ubers.☆ Two Darkrai's on the same field that learn Dark Void to put both your Pokemon to sleep and with Dreameater, Nightmare, and Dark Pulse. And lose twice as much damage because of both Darkrai's special. )= ☆
I frequently employ that strat in Plat. Dark Void, Nightmare, then Nasty Plot until first Pokemon dies. Repeat, only this time, I use Dark Pulse to instantly kill subsequent Pokemon. For Shoddy, I replaced Nightmare with Sub to ensure I get some Plots off.
I've 6-0'd in Ubers using that set. It's cheesy as hell, but it's effective if your opponent is too dumb to switch out, 'cause Sleep Clause ruins the strategy.