This is more of a concept than a dedicated Imposter counter, but it's still legitimate. It involves using Pokemon that can hit themselves for super effective damage. Since this is very basic, I'll jump straight to a couple sets:
Kyurem-White @ Choice Scarf
Trait: Contrary
EVs: 252 HP / 252 Def / 252 SAtk / 252 SDef / 252 Spd
Modest Nature
IVs: 0 Atk
- Draco Meteor
- Overheat
- Volt Switch
- Trick
Scarf Kyurem-W makes for an incredible late-game sweeper, and with the Scarf it just blasts right through Imposter Chansey.
Archeops @ Life Orb
Trait: Magic Guard
EVs: 252 HP / 252 Atk / 252 Def / 252 SAtk / 252 SDef / 252 Spd
Jolly Nature
- Head Smash
- Brave Bird / Wood Hammer / Hi Jump Kick / Flare Blitz
- Brave Bird / Wood Hammer / Hi Jump Kick / Flare Blitz
- Magic Coat
Magic Guard Archeops is one of the most entertaining Pokemon to use in the entire metagame. A Flying-type that doesn't take damage from SR and has a chance to 2HKO Giratina using an unboosted neutral move (after SR)? Yes please!
252 Atk Life Orb Archeops Head Smash vs. 248 HP / 252+ Def Giratina: 214-253 (42.54 - 50.29%) -- 48.44% chance to 2HKO after Stealth Rock