Aggron Analysis

Aggron
Sturdy
OHKO moves will fail.
Rock Head
Recoil moves have no recoil.
Type Tier
Steel / Rock UU

Name Item Nature
SubPunch
Leftovers Adamant
Moveset EVs
~ Substitute
~ Focus Punch
~ Stone Edge / Rock Slide
~ Avalanche / Thunder Wave
252 HP / 252 Atk / 6 Spe
This is the old SubPunch standard from ADV, supplemented by the addition of STAB Stone Edge. Aggron is easy to get in, particularly on Choice Band Normal-types; it can subsequently set up a Substitute and attack away. Thunder Wave will let it outspeed opponents and also potentially set up a Substitute when it otherwise couldn't. Rock Slide is an option over Stone Edge for "paraflinch" with Thunder Wave, and has slightly better accuracy than Stone Edge. With a Sub for protection, you can strip off a good chunk of HP from Claydol and Nidoqueen with a boosted Avalanche.

Name Item Nature
Support
Leftovers Adamant
Moveset EVs
~ Stone Edge / Iron Head
~ Earthquake
~ Stealth Rock
~ Toxic / Roar
252 HP / 252 Atk / 6 Spe
Smart prediction against a Choice Bander lets Aggron come in with ease, so he is a fine candidate to set up Stealth Rock. Stone Edge provides the best coverage alongside Earthquake, although Iron Head is a better option against most Fighting-types and the likes of Claydol and Solrock. Toxic greatly hinders the tanking ability of Claydol, Quagsire and Blastoise (provided they don't have Rest), or you can opt for Roar to rack up some more residual damage once Stealth Rock is in play. You can Roar out Baton Passers like Dodrio, Drifblim and most Bug-types too.

Name Item Ability Nature
Choice Band
Choice Band Rock Head Adamant
Moveset EVs
~ Stone Edge
~ Aqua Tail
~ Double-Edge
~ Earthquake / Superpower / Focus Punch
152 HP / 232 Atk / 124 Spe
With Choice Band and the specified EVs, Aggron reaches an astounding 517 Attack. Aggron is easily capable of switching into battle thanks to its numerous resistances. Stone Edge is Aggron's main form of attack due to its high base power, good offensive typing, and STAB. Aqua Tail pairs nicely with Stone Edge, hitting those Pokemon hoping to switch into a Rock attack (Claydol, Nidoqueen, etc.) for super effective damage. It also hits Probopass and Bastiodon for super effective damage without the negative side effect of being locked into a Ground attack. Double-Edge is Aggron's most reliable method of attack against Gastrodon and Quagsire. Due to Aggron's ability, Rock Head, Aggron does not suffer recoil damage from the attack. The last slot is used to hit Steel-types that might prove to be an obstacle. Earthquake quickly disposes of Probopass while also maiming Nidoqueen and Toxicroak. Superpower and Focus Punch deal with Steel-types, but they are resisted by common UU Pokemon such as Venusaur, Nidoqueen, and Toxicroak. Just be wary of the Defense lowering side-effect of Superpower.

124 Speed EVs allow Aggron to outspeed those Pokemon with 65 base Speed that do not invest EVs in the stat, the most notable being Clefable. With 152 HP, Aggron will never be OHKOed by unboosted 252 Attack Adamant Life Orb Altaria's Earthquake, even when factoring in Stealth Rock. This means that Aggron can switch in after a teammate has been KOed or on a turn when Altaria is using Roost, survive the incoming attack, and OHKO with Stone Edge. The remaining EVs are placed into Attack.

Name Item Nature
Metal Burst
Leftovers / Focus Sash Relaxed
Moveset IVs
~ Metal Burst
~ Stone Edge / Iron Head
~ Focus Punch
~ Curse / Protect
0 Spe
EVs
252 HP / 252 Atk / 6 Def
Metal Burst is a neat move that acts like Counter and Mirror Coat in one, but it needs to go last in order to be effective. To this end, it is recommended that you have a 0 Speed IV, which leaves Aggron at 94 Speed, slower than practically everything (including most Snorlax, provided it hasn't used Curse).

If you're using this in OU, Focus Sash could give you a chance at countering boosted Earthquakes, Close Combats or Aura Spheres. It seems simple, but this set requires a bit of prediction to be effective. You'll want to use Focus Punch if your opponent attempts to boost their stats, and Stone Edge (or Iron Head, which hits most Fighting-types for neutral damage) to prevent them from using Focus Punch to dodge Metal Burst.

Curse in the last slot can help it to survive a physical attack (including an unboosted Earthquake from Garchomp, or DynamicPunch from Machamp), and the Speed drop all but ensures you will go last with Metal Burst. Protect can ease your prediction worries by scouting your opponent.

Other Options

Aggron learns Rock Polish, but the odds of sweeping with it are rather low. ThunderPunch can be ignored, as Aggron's other options will cause greater or equal damage to every Water-type he will face, barring Poliwrath. Fire Punch hits Forretress, Scizor, and Bronzong, but is rarely worth a moveslot.

EVs

Max Attack is recommended on most sets. For defensive sets (Sub Punch, Support), plenty of investment in HP is good. Max Speed on the Choice Band set will outrun Milotic by a single point, enabling Aggron to 2HKO with Stone Edge. More importantly, it allows Aggron to outrun most Claydol, Nidoqueen, and Blastoise.

For Metal Burst sets, go with max HP first. You'll want to be as slow as possible, so go with a Relaxed nature. Pouring all your EVs into Defense helps to survive more powerful attacks, for example a Close Combat from Choice Scarf Heracross fails to OHKO after a Curse if you max out Defense. You only need around 120 Defense EVs to guarantee you survive Heracross' onslaught so you can invest some more in Attack to beef up Stone Edge/Iron Head and Focus Punch.

Opinion

Aggron is a neat Pokémon with good stat distribution and a good movepool—it is just hampered by two terrible 4x weaknesses to very common attack types. It is usable in OU play, but it is in the UU environment where Aggron can be a real force, battering everything in sight with Rock attacks and Focus Punches from its impressive base 110 Attack.

Counters

Ground and Water-types, such as Blastoise, Sandslash and Quagsire, are effective. Despite Aggron's impressive Defense, Focus Punch (and other strong Fighting moves) will rip it a new one. Most unresisted special attacks will do good damage; just beware of Aggron's high attack power when using frail special sweepers. Claydol walls it unless it carries Ice Punch or Aqua Tail, and finishes off Aggron with Earth Power or Earthquake. Nidoqueen and Claydol wall Aggron's Fighting and Rock attacks, but both need to beware of CB Ice Punch, Avalanche, Aqua Tail, and in Nidoqueen's case, Earthquake.