Honestly simply pairing up Tentacruel and Ferrothorn with a Gira-O would be more effective as you have a bread and butter stall which will make for an infuriating inability to spin and leave your opponent watching in helpless despair as there team is slowly ripped apart by the residual damage. In fact a bit of personal advice, you may want to try out run of the mill stall because with the speedier meta it has become far more effective albeit tough to pull off. I have been using stall to great success because of how unprepared teams are for it. Anyway enough of my ranting.
On to the topic itself I have really enjoyed using...
Choice Scarf Mamoswine
He is actually really great at what he does. Choice Scarf lets him revenge kill a plethora of Top Tier threats like Groudon, Mewtwo, Dialga and a stack of Arceus formes. While it seems a little counterproductive to run Priority on a Choice Scarf user Ice Shard also sets him apart from the other scarfers as it lets him pick of faster scarfers like Zekrom or Garchomp. It also lets him revenge Ray without e-speed. If your in need of a revenge killer give him a shot he wont disappoint.