Supporting Mega Venusaur to S Rank
Mega Venusaur is truly metagame defining. Some pokemon run movesets just to beat this thing, or have a chance of beating it (ex keldeo running hp flying instead of something like hp electric). Mega Venusaur is able to beat the vast majority of the OU metagame in a 1 on 1 scenario with the offensive tank set. And when I say vast majority, I really mean it. Assuming Venusaur has an EV spread of 236 hp/252 spatk/20 speed modest nature and a moveset of Giga Drain/Sludge Bomb/Synthesis/Hp fire, Mega Venusaur beats the following pokemon 1 on 1:
Thundurus, Raikou (without extrasensory), Greninja (without extrasensory), Manectric, Zapdos, Keldeo, Azumarill, Amoongus, Breloom, Ferrothorn, Scizor, Landorus-t, Gyarados, Tyranitar, Mandibuzz (give Venusaur 0 attack IVs and foul play wont do shit then pressure it with sludge bomb), Gliscor, Garchomp, Manaphy, Excadrill, Diggersby, Clefable, Sylveon, Rotom-W, Suicune, Terrakion, Mamoswine, Infernape, Bisharp, Hippodown, Conkeldurr, Skarmory (without brave bird)
The things that do beat Mega Venusaur 1 on 1, have a very difficult time switching in on its powerful attacks. Latios, Latias, Pinsir, Medicham, Gardevoir, Alakazam, Charizard, Talonflame, Kyurem-b all take huge damage from sludge bomb (and risk getting poisoned). A bunch of those are also weak to SR, so after a SR switch in, they can even get koed. Heracross can't switch in that easily either, because the Mega Venusaur user can predict the switch in and 2hko Heracross with HP Fire. Landorus also takes massive damage from Giga Drain on the switch.
Very few pokemon outright wall Mega Venusaur's offensive tank set. The only two I can think of at the top of my head are Chansey and Heatran, and both of those can be beaten with the proper moves. Chansey does not like Leech Seed at all, and Heatran fails to do any significant damage to you but you can do massive damage in return if you run Earthquake.
S Rank: Reserved for Pokemon that are amazing in the OU metagame. These Pokemon are usually able to perform a variety of roles effectively, or can just do one extremely well. Their use has low risk involved and high reward exerted. Pokemon in this rank have very few flaws that are patched up by numerous positive traits.
Mega Venusaur, in my opinion, fits this description extremely well. Because it can beat the most of the metagame easily in a 1 on 1 scenario, and the majority of the pokemon that do beat it 1 on 1 don't like switching in on it at all, and its ability to customize its EV spread and movesets to better fit on the team its in, using Mega Venusaur has very low risk involved put at the same time has high reward. It has numerous positive traits and very few flaws (weakness to flying and psychic).
We need to look at how Mega Venusaur defines the metagame and how well it fares vs the rest of OU/BL. We are used to S Rank being the home of powerful sweepers or super hard hitting wall breakers. While Mega Venusaur may not be the most hard hitting pokemon or capable of sweeping entire teams (which is why this nomination might be controversial), its defensive traits combined with its power more than make up for this.
BUMP MEGA VENUSAUR TO S RANK