It's been mentioned before but Lati@s do not deserve to be in A+ anymore. A, maybe, but definitely not A+. This new generation has not been kind to them at all. Thanks to the buff in Knock Off and dark moves in general, all sort of nasty dark moves lay waste to Lati@s. In addition to dark moves being buffed, they suffer from the newly introduced fairy pokemon. Sure, there may only be a few fairy pokemon in OU, but their arrival into the meta-game has done Lati@s no favors. More so, the nerf to Hidden Power also hit them bad, Lati@s really does like that additional coverage granted from Hidden power. What did they gain in this generation? For me, their biggest gain would be their niche as an offensive defogger, which admittedly is a solid niche, but not enough to keep them in A+. I nominate Lati@s for A rank. They still have a great speed and Sp.Atk stat, along with some interesting support moves like Trick, Defog, and Recover. However, their typing was a bit of a liability last generation and their typing only became a bigger liability, being weak to the ever common U-turn and knock off.
Charizard-Y should be in A+, with it's fellow mega-evolution Charizard-X. Charizard-X may be the best dragon dancer in OU, but then Charizard-Y may be the best fire nuke in OU. With a base Sp.atk of 159 and a drought boost, I cannot think of ANY OU pokemon that isn't 2HKO by Charizard-Y's Fire Blast unless they resist it or are flat out immune to fire. For those pesky water types, Charizard-Y has access to solarbeam, which works perfectly with drought. And while he has a massive 159 sp.atk stat, his atk stat of 104 is definitely passable, allowing him to even run a mixed set. Pesky Heatran ruining your day? Hit it with an Earthquake.
0- Atk Mega Charizard Y Earthquake vs. 252 HP / 0 Def Heatran: 256-304 (66.3 - 78.7%) -- guaranteed 2HKO after Leftovers recovery
Even with no atk investments and a negative nature, Charizard-Y still 2HKO specially defensive Heatran.
0 Atk Mega Charizard Y Earthquake vs. 252 HP / 252+ Def Heatran: 204-244 (52.8 - 63.2%) -- 99.6% chance to 2HKO after Leftovers recovery
Physically defensive Heatran doesn't do much better. As long as Charizard-Y has a neutral attack nature, he's almost guaranteed a 2HKO. And this is all assuming rocks or spikes aren't up. If they are, it'll be an easy 2HKO all the time.
I don't get exactly what makes Charizard-X better than Charizard-Y. Granted, they do different things, but they're both one of the best at what they do. For Charizard-X, that would be dragon dance sweeping. For Charizard-Y, that would be wallbreaking.
Chansey is many things, but A rank isn't one of them. Easily THE best special wall in the game, Chansey could also make for a mean mixed wall. He's really good at soaking up attacks... and that's it. Chansey is set-up fodder. Yeah, he can try hitting something with Seismic Toss, but that's pretty much his only form of offense. Ghost pokemon would have a field day with Chansey. Maybe Chansey can also paralyze them? Not like Aegislash would really care. And something like Gengar would just set-up a sub right up in its face. The support that Chansey grants to her team is undoubtedly great, passing massive wishes or being the team cleric with heal bell. Heck, Chansey can even be the SR setter. However, it's extremely clear that if Chansey packs an attack, the only attack it would have is Seismic Toss, which would deal a flat amount of damage. Chansey's offensive stats are absolutely abysmal with a low speed, making it unlikely to outspeed anything. Taunt makes Chansey almost all, but completely helpless. It actually somewhat baffles me that something like Skarmory (probably the best physically defensive wall in the game) is ranked lower than Chansey. Skarmory may not be particularly strong, but at least it's not as much of a set-up fodder as Chansey. Also, if Skarmory loses his item, he's not hurt as bad as Chansey. If poor Chansey loses his evolite, he becomes inferior to Blissey in every matter. I nominate Chansey for B+ rank.