Role: Bulky Lead / Tank
Trait: Sturdy ------> Filter
EVs: 252 HP / 16 Def / 240 Sp. Def
- Stealth Rock
- Thunder Wave / Roar
- Metal Burst
- Head Smash / Earthquake / Stone Edge
Mega-Aggron is a lot like Mega-Steelix, but better. First off, its amazing Filter ability allows it to take less damage from super-effective attacks. Mega-Aggron's pure Steel-typing also gives it a plethora of resistances. In addition, it gets good Utility moves, such as Thunder Wave. Finally, it has an above average 140 base Atk and a sky-high base Defense of 230!
EVs are needed to give M-Aggron decent bulk. Because of its already high Defense, it needs minimal investment. The EVs in HP and Sp. Def help it to take Special Attacks better. Impish nature is required to further boost its Defense.
Stealth Rock is almost always a mandatory on Aggron.
Thunder Wave can cripple sweepers, while Roar gives M-Aggron an opportunity to rack up as much as damage as possible.
Metal Burst is a good move because Aggron can tank a move and retaliate back with a more powerful attack.
Head Smash gets good damage, but has a nasty recoil and doesn't get STAB when you mega-evolve. Stone Edge is a better alternative for avoiding recoil, but still does decent damage. Earthquake provides good coverage and deals with other Steel-types that can wall this set (ex: Ferrothorn).
This set is primarily designed to be used as a bulky Lead, but it can also be used mid to late-game. In certain cases, you should hold off Mega-Evolving Aggron. For example, to avoid a super-effective Fire attack, you shouldn't Mega-Evolve and take neutral damage instead. Also, use Roar only on certain Pokemon. If you predict a switch-in, use a super-effective attack.