A lot of these posts I've been reading in this thread are so wrong...
Metagross does NOT stop dual screen Deoxys-E. How do you stop it? Prayer... or Brick Break.
Deoxys-E is THE most gamebreaking pokemon in OU. Period. No ifs ands or buts.
He has unpredictability and speed that Gengar dreams of, and the best movepool in OU. So how do you stop it? Well, you have to know the set. And seeing how he's faster than you, switching out means you've given him TWO turns to do what he wants to do.
Dual Screen Deoxys-E - is flat out Uber. I run it in ubers and it works just as easily there. Theres no way to beat it. You can brick break, but he can just through up another screen and stall your pissy weak brick breaks out of PP with pressure. Explosion is horribly predictable and after reflect, he survives that too. There is no way to stop it except, Night Slash Choice Scarf Weavile could do the trick, but that is overcentralization at its finest. I've seen Choice Scarf Jolteon's and Weaviles lately just for Deoxys. Pokemon of the top 2 speed tiers in the game. This is fucking ridiculous!
Sweeper Set - Spritomb and Cresselia are your best bets. Dugtrio makes a good revenge killer with sucker punch, as does a Hounchrow with Sucker Punch AND pursuit. Bulky steels work somewhat ok, but a lot of Deoxys-E are paired with Magnezone and / or residual damage. I wish people would start being more diverse with this set. I know I rely on Scizor to counter Deoxys, so I put Fire Punch on my own and fried so many Scizor and Forry. Swampert is an alright counter, but Deoxys-E can Grass Knot and Swampert can't even OHKO back. My famous Impish, Max Defense Snorlax makes a fantastic counter as Superpower is a 3HKO with attack drops. Quiet as kept, Careful Steelix (I used extensively on my Brock theme team) is a FANTASTIC counter, being 4HKOed by anything Deoxys can throw at it with Life Orb. And after the defense drop of superpower, EQ is a KO.
Cosmic Power / Taunt - Explosion + Priority move.
Spiker - Rapid Spinner
Rain Starter - No counter, it did its job before you touched it.