I definitely think day dog will be better than night dog, but in both cases, mono-rock is such a shitty typing. Offensively, sure, day dog will be able to pick off zard and talon, which is cool, but it just seems to me that almost every team except for hyper offense is carrying hippo, ferro or some other bulky rock resist that I just don't see day dog being able to break. Sure, there are other attacking rock types in OU, but Tyranitar and Terrakion both have awesome secondary attacking STAB moves and mega Aero has a bunch of decent coverage moves that it's picked up across the gens, most of which are boosted by Tough Claws. At least for these games, I think it'll be quite likely that day dog will have poor coverage owing to there being no move tutors and it's got no secondary STAB to fall back on.
On the flip side, night dog also has all these problems and is also likely to be rather slow just based on its design, its description and how they presented it in trailers. If it were a dark type with Swords Dance and sucker punch then we might have been in business, but alas, it isn't a dark type, and while it might have Sucker Punch that's not that great without STAB, and for a tanking style pure rock is just raw shit, it gives it so many weaknesses and not that many good resists. Also while Vital Spirit isn't a terrible ability, it's not going to be beating any of the common sleep setters in OU so it's pretty pointless.
Neither of these forms have too much future in OU, I feel. Sand rush and accelrock might give day dog some niche uses, but at the end of the day both are likely to be free switch ins for top tier OU threats like Keldeo, Landorus, Breloom etc, which will send both of them scurrying for cover. I see day dog maybe being mid-to-low UU and I'll be surprised if night dog is any better than NU. It's annoying because it's carrying on the trend of most new mons since gen 5 that aren't megas being pretty shit.
