OMG, can we please not start the Manaphy debate again? It's been like two weeks since that long trite and we have more than 10 pokemon of interest before we need to consider tackling that again...
And while its not on topic either, I don't support M-Gyarados to S rank. There's no need, it is roughly as effective as it has ever been and A+ is in fact being a bit generous for it. I'd sooner support a drop than a rise but I actually think its fine where it is. It's ironic really, because Gyarados dominates Stall with Taunt sets and Offense with Sub sets, but balance is actually tricky as neither set is as reliable and it requires more team support to really sweep. It's more of a tank really as even with a DD in it still doesn't always feel super fast and the low BP of its STABs means it isn't one shotting many neutral targets even with a boost. Compared to Char-X and M-Altaria who have much higher BP moves, better STABs, and better defensive typing and auto recovery, pretty much means they will and should always be ranked higher than Gyarados itself. Still, Crunch and Waterfall are reliably accurate and have awesome side effects, Gyarados loves having Intimidate before hand and can actually get away with remaining in its base form if need be, which is always fun, and Mold Breaker is still excellent. Great mon, a fave of mine to use, just not S material.
Mega Metagross - I've oscillated back and forth whether it should drop or not, which is funny because I never actually though it deserved S in the first place, mainly because of its horrible STAB combo, no recovery and paltry boosting options compared to Altaria and Char-X. Still, its hard to ignore those phenomenal stats and offensive coverage. But yeah, I think status flying everywhere and Spikes being popular are bad news for its bulk, as if you don't get a Mash boost or have the right coverage you can often be forced out to take more hazard damage, statused and crippled, or simply revenge killed. Yeah, it's time, drop it to A+
Mega Diancie - If I think Metagross should drop down, then to be consistent I think Diancie should drop as well, as I also never really agreed with A+ for it and Diancie is just not on Metagross' level, or Mega Scizor for that matter. I'll be honest, I'm having trouble qualifying that statement, so forgive me if I don't sound terribly convincing.
Ferrothorn - It's always been a solid mon with great typing, but similar to Rotom-W, it can find itself taken advantage of. Next to Skarmory and Chansey this thing is like the biggest Taunt bait, often carrying only a single attack, it often gets its Leftovers Knocked Off, and so many things carry HP Fire specifically for it and Scizor. It very often gets things accomplished and is a good road black for many offensive types and a good Rain check, but like Rotom-W it is still viewed as a nuisance more than a threat. I vote to stay in A
Keldeo - I've never seen this thing as S, I still don't, even acknowledging and appreciating the diversity of its sets, utility and power. But I view all of these positives very similarly as I do Talonflame. These two are surprisingly bulky for fast offensive mon and haze such great power even when you don't invest in offenses. They are the creme of the crop, and likely always will be, but not S material. Keep Keldeo in A+
Gengar - Like the other two, I view Gengar in a very similar vain and pretty much the epitomizing representation of A+ class. While not bulky, with its three immunities and access to fast subterfuge options like WoW, Taunt and Disable it can be surprisingly resilient. All while sitting at the crucial 110 speed tier and having just phenomenal offensive and niche STABs. And like the other two, it has sets out the wazoo, in fact, at least twice as much I'd say! It faces zero competition as a Ghost type as outside of Mega-Sableye, who you can't run if you want a different mega, the closest thing is Gourgeist all the way down in C rank! Unlike some pokemon in A that I view as a nuisance, I legitimately am weary when I see an opposing Gengar, as outside of max speed, you don't know WHAT its running. And it can be something as simple as using Destiny Bond when I try to Pursuit trap with Bisharp that ends up costing me big time.
Celebi - Again, this thing should NOT drop and stay A-. I mean really, a simple SpD set with Thunder Wave/Earth Power, Giga Drain, Nasty Plot and Baton Pass/Earth Power is so deadly. +2 Earth Power destroys would-be threats like Heatran, Tentacruel, Dragalge and Bisharp (who would never use Sucker Punch, almost always Knock Off or Pursuit), and +2 Giga Drain with a Calm spread is offensively potent and easily lets you win against other special pokemon like Clefable, Manectric, Raikou, Sylveon, Reuniclus, Slowbro/king, etc. It's also one of the best Rain checks you could have and is such a good partner for offensive Fire types, particularly Char-X. It's niche is too useful, supporting and handling so many common pokemon that OU staples have trouble with.