Shield Dust
Tough Claws
Defiant
Comatose
I'm actually most fond of Shield Dust because that helps negate the secondary effects of stuff like Toxapex's Scald, Arghonaut's Gunk Shot and Knock Off, and Tomohawk's Air Slash, all of which could potentially cause a lot of trouble otherwise for something that's supposed to hard counter them. Tough Claws also gets my support due to the possibility of running Anchor Shot, which may be useful as an anti-Fairy coverage move, though the fact that it doesn't affect Spirit Shackle is worrying; Defiant, meanwhile, may also be a useful clutch ability in case of attempts to whittle away at CAP's defenses or slow it down, because I can see it being targeted on sight if its trap moves are going to be an issue. I can certainly understand the appeal of Comatose, but at the same time I feel it may become predictable after a while, because soon the status immunity may prompt opponents to simply use STAB or even strong neutral damage to take CAP out of the equation before it causes trouble, and seeing as Arghonaut and Tangrowth occasionally run Knock Off, that could be a problem.
About the only ability that I'm not including in my vote list is Strong Jaw, since I don't see its relevance here - none of the biting moves available are STAB and if Strong Jaw were chosen they'd probably would only be viable for coverage purposes. If there were moves that could work with both it and the concept we're going for I'd be more in favor of it, but as it stands it doesn't really add to the concept if all it's good for is taking down just a few things on CAP's hitlist that aren't covered by its STAB.