The key to counter Revenankh is to act quickly. If you see Revenankh switching on something that will give it a free Bulk up whether you switch or not, don't hesitate, and SWITCH. Revenakh doesn't have many counters when it has 6 Bulk Ups on its sleeve.
What? You say I'm stating the obvious? Well, this seems to be the problem with many people, so I guess I'd say it anyway.
And Revenankh is not better than other dangerous threats that can set up. You don't let a Garchomp Swords Dance freely if you can stop it, right? Because, you know, Hippowdon can counter SD Chomp, but not if Chomp has 3 Sword Dances under its belt. Or Dragon Dance Gyara.
And if your excuse is that you can't incorporate a Revenankh counter into your team... Well, it's your fault. The DP metagame has already enough threats to stop anyone to get a counter for everything. CAP is only adding to the list. But Revenankh is definitely counterable, if you want to carry one of its counters. Togekiss is great and counters Revenankh greatly. Revenankh needs like 3-4 Bulk Ups to start having a chance. Staraptor, Yanmega, Psychic Celebi, CM Cresselia, Psycho Cut Medicham... All can beat Revenankh one on one after even one BU, more in most cases.
At first I thought Revenankh was too powerful, but now I just think it's dangerous. But DD Gyara dangerous, not even SD Chomp dangerous.