Enough talk about our system of separating MEvos. The Uber viability ranking thread can do whatever they want, this is not an argument for this list to do the same. We know the reasons to rank the MEvos seperataly or treat them as the same Pokemon, so if we feel that there is a need to change the system, we will do it. Posts talking about how we should change this system in this thread will get deleted from now on. If you want to present a good reason as to why we should change the system that hasn't been mentioned before, feel free to PM any of the OU mods.
On to the the Pokemon in S and A+ ranks now.
Drop Mega Venusaur to A+
The metagame has reached to a point where it's overprepared for Mega Venusaur, and this means that Mega Venusaur can't wall the majority of the metagame anymore. Mega Venusaur can't wall a single Pokemon from S rank, and the majority of A+ and A rank Pokemon can get past it too. Out of A+ and A rank, Mega Venusaur is a good answer to: Manaphy (without Psychic), Rotom-W, Thundurus, Azumarill, Mega Gyarados (without Ice Fang), Keldeo, Mandibuzz, Conkeldurr, Mega Mawile, and that's it. Yeah it can check some more Pokemon in those ranks depending on their movesets (Extrasensory-less Greninja, AV Excadrill, Terrakion without LO or CB), but those Pokemon can at worst 3HKO Mega Venusaur while outspeeding it, or have other means of wearing Mega Venusaur down (U-turn on Greninja). Not only this, but if you are using Mega Venusaur as your answer to Rotom-W, which you most likely will be as Rotom-W is not an easy Pokemon to shut down, chances are that Mega Venusaur will get burned very early in the game. Combine this with potential SR damage, and Mega Venusaur is taking 25% damage minimum every time it switches in, without accounting for Volt Switches from Rotom-W or U-turns from Greninja. Furthermore, Mega Venusaur has pathetic longevity against sand teams, which are better than ever right now, as one of their biggest problems is out of OU (Mega Lucario). For example, Choice Specs Keldeo on a sand team dgaf about Mega Venusaur, as all it has to do is hit it once with Hydro Pump and then it can 2HKO it later, as Mega Venusaur will manage to heal 19% at best with Synthesis after sandstorm damage as you go to a Pokemon that forces it out. This is a huge problem with Mega Venusaur and can't be understated. If you have some Pokemon that are completely shut down by Mega Venusaur in your team (and there are not so many of them out of S and A ranks, aka the best Pokemon in OU), it is not hard at all to wear down Mega Venusaur to the point where it can't stop those Pokemon. You can use WoW Rotom-W with good SR support, a Volt-turn core with SR support, a sand team, a lure (such as Psychic Manaphy or Nasty Plot Hidden Power Flying Thundurus), or a rain team. Honestly, there are so many ways to get past Mega Venusaur, and you often don't even have to choose one of them as Mega Venusaur fails to wall more than 1-2 Pokemon against most teams. Without Mega Lucario terrorizing OU and Mega Venusaur being one of its most viable checks, Mega Venusaur has no reason to be in S rank.
Promote Rotom-W to S
This is going to be a tough one but let's give it a try. No, Rotom-W doesn't wall the majority of the metagame, and no Rotom-W is not hard to wear down and overwhelm. But Rotom-W is the single best Pokemon in OU when it comes to utility and support (together, not seperately). Remember how Genesect could get an advantageous match-up against most of the metagame and use this to its advantage to start generating momentum and give free switches? Rotom-W is the next best Pokemon at doing this, and while its ability to generate momentum is certainly not at the same level as Genesect's, it makes up for it with the amount of Pokemon it checks. When Rotom-W gets an adantageous match-up, it can either bring in of your Pokemon for free with Volt Switch as the opponent switches out, OHKO/2HKO the incoming Ground-type with Hydro Pump (except from Gastrodon), or cripple the opponent with WoW, which when coupled with future Volt Switch hits and SR, is a very effective way to wear down even the best checks to Rotom-W, such as Mega Venusaur, Latios, and Latias. So no matter what happens, Rotom-W will always be able to do something productive with the switches it forces, even if the opponent has hard counters to it. It will always be able to give immense support by providing free switches to your teammates while spamming a decently powered STAB move or punish the Ground-types that may want to block your Volt Switch. Furthermore, Rotom-W serves as a good check to a multitude of great and common Pokemon, such as Mega Pinsir, Heatran, Talonflame, Landorus, Landorus-T, Garchomp, Azumarill, Sand Rush Excadrill, Greninja, Mamoswine, Mandibuzz, Scizor, and Hippowdon, and wins 1 on 1 against even more Pokemon, giving it a plethora of chances to support its team, by either bringing in other Pokemon for free, or wearing down checks and counters of its teammates. How many times have you seen on an analysis the phrase ''Even though powerful, this Pokemon is frail, so Rotom-W is a great partner''? We may have become used to it and think it's not a big deal, but take a moment to think just how many frail but powerful Pokemon rely on Rotom-W's Volt Switch to switch in. Think about how much damage those Pokemon are able to do after Rotom-W brings them in for free. This, right there, is some top notch support, which when combined with the defensive utility that Rotom-W provides for a team, makes it worthy of the S rank status.
All the other Pokemon are fine where they are.