Mega Aggron: C- Rank ---> C+ Rank
Mega Aggron is severely underrated right now, and it is most definitely not C- Rank. Lately, I've been using it a bunch on an offensive team with a spread of 252 Atk / 4 SpD / 252 Spe and an Adamant nature. "But unfixable! What kind of spread is that?" Well, dear friend, it's a Rock Polish set! You may be thinking: has he gone mad? Rock Polish Mega Aggron? Why yes! I've been using Rock Polish Mega Aggron lately and I'm so impressed. People are overlooking how it has an Attack stat of
140. That's very big, and is only 5 less than Landorus-Therian. Now you're looking at its base 50 Speed. What does that outspeed? Everything up to Adamant Mega Aerodactyl! A set of Rock Polish | Heavy Slam | Ice Punch | Earthquake is able to effectively hit everything at least for neutral damage in OU, bar the incredibly common Surskit. Heavy Slam is insanely powerful, and Mega Aggron is very very heavy, so many things will be hit for a large sum of damage. It's best left for late game, after the opposing team is weakened. Without investment, Mega Aggron isn't even going to be bopped by physical attacks. Choice Band Terrakion doesn't even KO after a layer of Spikes, for example! The icing on the cake, in my opinion, is its excellent synergy with Celebi. Celebi is so powerful to combine with because it passes a Swords Dance onto Mega Aggron. This is just so amazing, and the strategy has been performing very well. I think Mega Aggron's so powerful and has excellent opportunities to set up. However, Mega Aggron faces competition from Mega Metagross because it, too, has Rock Polish. Using Mew as an example, it takes 66.8-78.5% while Mega Metagross does 62.4 - 73.9%. Against a lot of foes, Mega Aggron will be more powerful because it can run an Adamant nature. In comparison, Meteor Mash does 117 and Heavy Slam does 120 (to most foes). Is this big enough? Not really. But, it does have perfect accuracy which is probably a niche enough. Mega Aggron's synergy with Celebi and ability to set up Rock Polish on a variety of foes, unlike Mega Metagross gives it a respectable niche and I think it definitely deserves the raise. I really don't feel you can compare Mega Aggron to Noivern, Zygarde, and Espeon, who all receive much larger competition and opportunity cost than Mega Aggron. Mega Aggron's possibly not a C+ Rank threat, that could be an over exaggeration, but I do feel C- is not doing Mega Aggron justice. Instead, a high placement is in order for it.
Here's a replay of Mega Aggron in action:
http://replay.pokemonshowdown.com/ou-221602450.