So I tried the Specs set with rain support for a bit and goddamn does it hit like a nuke. Just about anything that does not resist Water is flat-out OHKO'd by rain-boosted Specs Hydro Pump. You're pretty much limited to Lati@s, Serperior, Jellicent, etc. to take one and not kneel over dead. Weather starters can mitigate the effects but none of them like taking STAB Secret Sword to the face (same goes for BlissChan), although that does make you Chandelure bait (not that your average Chandelure is ballsy enough to switch into Keldeo but you get the point). Hydro Pump / Secret Sword / HP Ice / Surf seems to me to be the best moveset, but if you're weak to Jellicent or Toxicroak you could go for HP Ghost / HP Psychic respectively (I don't really recommend that though). It's more suited for hazard dependent teams that CM Keldeo, since it focuses on pummeling things right off the bat. Spin support is cool too since this version switches out far more frequently than CM Keldeo.