I don't see how this is or could ever be a remotely viable set. Firstly, Nature Power. In Generation VI, Nature Power is never Physical, and in competitive environments Nature Power is by default Nature Power, which neither adds more coverage, nor is it seemingly worthwhile to support it with Terrain moves as they themselves are not very useful. While Carbink is generally Bulky, 50/150/150 Defenses are only slightly better than 100/100/100, and that's easily 2HKO-able with Super Effective moves, not to mention no recovery whatsoever. It maxes out at 218 Sp. Attack, which is so Pathetic that it's almost if not more vulnerable to setup than the vast majority of defensive Pokemon, the only difference being it wastes more moveslots to potentially hit others Super Effectively. In this sense it is outclassed in almost every way, even in the lower tiers.
