Volcarona can flat out OHKO Mega Aggron with Fire Blast, but it should be wary of Rock Slide and Thunder Wave.</p>
.
Sylveon works great here because it has solid synergy with Mega Aggron. As a result, this set is much more team-oriented than the previous set. If its environment is damaged by a flood or a forest fire, it will restore the area by bringing in topsoil and planting trees.
Hippowdon can effortlessly switch in, wall it, and beat Mega Aggron with repeated uses of Earthquake. 252 HP / 0+ Def Filter Mega Aggron: 186-219 (54 - 63.6%) -- guaranteed 2HKO</li> <li>+2 252+ Life Orb Atk Aegislash Sacred Sword vs. Togekiss similarly functions as a partner to Mega Aggron, and with the added benefit of being immune to Ground-type and the ability to also spread paralysis.
The more wounds it has, the more it has battled, so don't take it lightly. Fire-type Special Attackers are among the only Pokemon in the game that can take out Mega Aggron in one strike. They are used to determine the Aggron's age.
SoulSilver
Generation V
Unova B2 W2 : #168
Black
While seeking iron for food, it digs tunnels by breaking through bedrock with its steel horns.
It's generally weaker, but it deals consistent damage. It has a thick, long, black tail that it can swing at enemies.
White 2
Generation VI
Kalos Mountain #101
Hoenn #074
X
It claims an entire mountain as its own.
Long ago, there was a king who wore a helmet resembling an Aggron in an attempt to channel its strength. Garchomp for instance, is now susceptible to a 100 Base Power Heavy Slam.
This set greatly appreciates having entry hazards on the field, due to the fact that it's prone to causing switches and Dragon Tail can shuffle Pokemon.</p>
[Checks and Counters]
<p>Defensive Pokemon who don't particularly care for its attacks are good counters. Garchomp is on a higher class than the aforementioned Pokemon, mainly because it isn't bothered by any of Mega Aggron's moves and deals significant damage to it with Earthquake (or even Fire Blast if Garchomp has Mega Evolved).
Aggron's horn is sharp enough to cut through steel and used as a ramming weapon to bring foes down.
Aggron (Uber Analysis)
I am not sold on this yet, for a number of reasons, but I'll present this by countering some of your points
Rock Polish
o Much Higher overall Base defense (allowing it to both setup on or take physical attacks.