My first nomination, here goes nothing!
I'd like to discuss
Hippowdon and move him to
A Rank
While not really a pokemon with a solid presence in the entire XY OU generation Hippowdon has gained the attention of many Top Players lately, it is not difficult to see why, access to a solid recovery, great offensive and defensive type, Stealth Rocks something that every team needs, a powerful STAB in Earthquake, Whirlwind in order to not make him total set up fodder and even coverage moves like Stone Edge/Rock Slide and Crunch for Talonflame/Thundurus and Gengar respectively, 108/112/72 defenses grants him the ability to shrug off majority of physical attacks in the tier, an example would be the infamous Mega Metagross, which needs Grass Knot in order to muscle past him, Hippowdon also laughs at common Offensive 'mons like Mega Lopunny and Bisharp (he can even take a neutral +2 Life Orb Adamant Knock Off, something that many few pokemon can boast to do so) Mega Charizard X (a +1 Flare Blitz will do 65-76% to the on-site spread, while Earthquake + recoil will ohko) and can go toe to toe against many other rampant threats like Talonflame and Excadrill, even bulky enough to not get 2hked by LO Exca's EQ or Mega Pinsir's Return.
The special bulk while lower is also not really a pushover, the on-site spread allows Hippowdon to only have a very low 4% chance to be 2hked by Life Orb Gengar, one of Stall's greatest nightmares, also able to stop Thundurus or Volturn chain created by manectric due to the ground type and its bulk, if we were to give him more Special Defensive evs he would also be able to come in against Mega Diancie's Moonblasts much more easily, which is a great feat itself, testament of Hippo's bulk, and usefulness on a team.
And while Sand Stream is a great ability, helping inflicting residual damage and also stopping Drizzle/Drought, players can also opt to run Sand Force on Hippo, giving their team an easier time, which is very important, especially if you are using stuff like Mega Sableye, Mega Venusaur, Defensive Zard X or Mega Altaria.
Basically, Hippowdon has become a great glue on Balanced and Semi Stall teams (heck, you may even add him on bulky offensive teams as a glue and Stealth Rocks user), able to set up stealth rocks, stopping all Volt Switch users bar Rotom-wash, and able to take on a good chunk of the Metagame, making him an invaluable team player and a force to be reckoned on the Metagame (tbh much more than stuff like Mega Gallade which sits on A Rank, but that's another tale).