An archetype I've been seeing sometimes is Cresselia with Sunny Day accompanied by Latios with Protect, Solarbeam, Fire Blast and Draco Meteor and backed up by some Chlorophyll such as Shiftry. Really annoying if you ask me. Cresselia can't usually be OHKO by the Kingdra I'm using for my Drizzle strategy, and I find myself switching Politoed in and out all the time.
About Sleep tactics bacon spoke of, they definitely are dangerous, but they can easily be countered (I think). A somewhat-good defender with Spore such as Amoonguss might prove troublesome, but generally Pokemon that can cause sleep are not very hardy and are often countered by their move's accuracy (Hypnosis, Sleep Powder). Besides, the former biggest Sleep abuser, Dark Void Smeargle, is banned from VGC.