This isn't a joke, so don't laugh.
Nosepass @ Eviolite
Trait: Magic Bounce
Before we begin there are two things that are needed for this to be successful. 1) Sand Stream in effect, and 2) Stealth Rock + Toxic Spikes (Spikes isn't necessary but it's nice as well). CB Terrakion is actually still great in BH so I use it as a Sand Stream CB'er. For Toxic Spikes you can really use what you want as long as it's not something that attracts Magic Bounce users (i.e. something usually offensive / not used for hazards). Once you get those down you're pretty safe since the only Poison-type I've seen in BH is Gengar.
After one Cosmic Power, your Nosepass has 264 HP (bad), 831 Def (great), and 1047 SpD (great). Compare this to Cosmic Power Magic Bounce Lugia, who after one Cosmic Power has 416 HP, 591 Def, and 611 SpD. The only thing Lugia beats Nosepass in is HP.
Roar seems to be better since it can hit through Sub, but Dragon Tail is possible in its place. Clear Smog stops boosters of any kind and Roost keeps Nosepass alive. I guess you could use Recover, but Roost is much funnier. Clearly this Pokemon needs support to take care of whatever the final Pokemon might be, so I recommend something HO to go in your last slot, which is why the CB Terrakion I mentioned earlier is great. It outspeeds a majority of the BH'ers and usually won't have trouble destroying the opponent due to Clear Smog taking away any boosts to the defenses.