I've been running this set since the very beggining of bw2 really, does great. I know I'm not the only one to use it, WhiteDMist has also told me he used it with success.
Carracosta (F) @
Rocky Helmet
Trait: Solid Rock
EVs: 252 HP / 252 Atk / 4 Def
Adamant Nature (+Atk, -SAtk)
- Waterfall
- Stone Edge
- Aqua Jet
- Stealth Rock
Rocky helmet works pretty well on rock types in general because of there big defence, thier resistances that often leads to a switch-in on a contact move and since people often try to kill it off with fighting moves. Carracosta uses it even better than the other rock mons because of solid rock and access to aqua jet. Solid Rock means carracosta is one of the few rock types to actualy have the capacity to tank certan fighting moves such as cb braviary' superpower. Rocky helmet makes pretty massive damage for an item (1/6 of max hp !), and taking 2 hits instead of one can make a huge difference on how the game will turn out. Carracosta also has access to a priority move in the form of aqua jet. With max attack investment, the big turtle can add up to the damage it deals with rocky helmet to take down some of the most threatening things out there (let's not forget superpower and close combat come with a defence drop). Aqua jet being a stab water move also hits hard ground types that will just EQ carracosta without touching it's helmet.
This carracosta works extremly well to take down stuff like zangoose and braviary before they make huge holes in your team. (It might cost you costa's life though)
There's another item I'd like to put to the light, even though I have no particular pokemon to suggest it with, I think I can describe what kind of pokemon it helps. That item is the quick claw.
Unlike in other gens, quick claw has a 20% chance of making you attack first (instead of 10%). Using it may be completely relying on hax, but hey why do people use scald over surf ? 20% chance is decent enough to let some slow pokemon shine a bit more. The awesome thing about the quick claw is that it's never ever ever expected. The item doesn't fit every slow pokemon however, keep those lefties on amoonguss, a priority giga drain has very few chances of being game changing. Quick claw mostly fits the slow hard hitters, stuff like gigalith, relicanth, torterra and others. These pokemon usualy stay around long enough to abuse the 20% chance to it's maximum and hit so freaking hard, it's nearly sure you're making a difference with that priority head smash eq or whatever attack you're using.
Personaly, I wouldn't be using quick claw on something that already has priority because you could be using another item better, I also wouldn't use it on things that use encore and maybe healing moves, because attacking first could ruin your own predictions. Recovery could still help you stay around even longer to prey for that claw to activate at a crucial time (and who know's it could save your life when you were about to sac that poke). Same for volt switch on ampharos and eelektross, it might not give you that needed momentum if you attack first.