Volcanion @ Air Balloon
Ability: Water Absorb
EVs: 248 HP / 252 SpA / 8 SpD
Modest Nature
IVs: 31 Atk
- Steam Eruption
- Overheat
- Flash Cannon
- Earth Power
Volcanion demonstrates a few ways for mons to exploit the mirroring mechanic -- its ability grants it immunity from Steam Eruption while also healing damage, it takes extremely little from Overheat and Flash Cannon, and Air Balloon can grant (temporary) immunity from Earth Power. Overheat's Special Attack drop also greatly hinders opposing special attackers.
As a side note, you have to manually give special attackers 31 Attack IVs if you want to boost their damage output from mirrored physical moves, otherwise the teambuilder will set it to zero.
Tornadus (M)
Ability: Defiant
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Defog
- Acrobatics
- Superpower
- Knock Off / Taunt
Tornadus Incarnate can get a +2 boost off of a mirrored Defog, then use Acrobatics at twice the power of its opponent. Superpower can still be risky, but the defensive drop your opponent incurs will cancel out your lowered damage output until they switch. Since Tornadus has no item of its own, it's free to run Knock Off without worry of losing anything from the mirror, or Taunt if you need that more.
Rhyperior @ Choice Band
Ability: Solid Rock
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Stone Edge
- Earthquake
- Fire Punch
- Thunder Punch
There's nothing tricky going on here, just a powerful physical attacker that has the bulk to take what it dishes out. Even if it eats its own Earthquake on the knockback, it won't deal too terribly much unless it comes from another Ground-type.
Ferrothorn @ Rocky Helmet
Ability: Iron Barbs
EVs: 248 HP / 8 Atk / 252 Def
Relaxed Nature
IVs: 0 Spe
- Power Whip
- Gyro Ball
- Leech Seed
- Toxic
Probably one of the more evil sets you can run. Pokemon with abilities triggered by contact can force them to activate by using contact moves of their own; here, Ferrothorn takes almost nothing from its own attacks while dealing serious chip damage to its opponents
in addition to their natural damage. The last two slots go to moves that Ferrothorn can click with impunity that deal
even more residual damage.