Spiritomb@Leftovers
Trait:Pressure
EVs: 252 HP / 242 Def / 4 SAtk
Bold Nature (+Def, -Atk)
-Rest
-Sleep Talk
-Calm Mind
-Dark Pulse
Spiritomb's rather interesting stat distribution lets it carry a variety of useful sets, but this one really just gives zero f%^#s about Golurk. Being immune to that scary Focus Punch and being bulky enough to make sure anything else is at least a 3HKO (Earthquake: 38.82% - 46.38% | Shadow Punch: 27.96% - 33.55%) whereas a +0 Dark Pulse hits back for 51.05% - 60.47% (and +1 for a beautiful 76.18% - 90.31%).
It's a shame that Spiritomb isn't a little faster so you could guarantee setting up right away (while awake) but with Rest+Leftovers you can stall Golurk out indefinitely and set up while asleep. Also, don't forget about Pressure, it may not seem like much, but it adds up.