AnnoyLass
Someone on Random Matchup Single Battle destroyed my Metagross and Wobbuffet with this set. Credit for this set goes to whoever I battled. It is important to note that they came in with hail support, courtesy of Snow Warning Abomasnow, so if you don't have that you should replace Taunt with Hail.
Ability: Snow Cloak
Item: Leftovers
Moves: Substitute
Swagger
Double Team
Taunt/Hail
The idea of this set is to first use Substitute, then Hail (if you don't have hail support) (to activate Snow Cloak and do damage)/Taunt (to prevent accuracy boosters and Safeguard users), then Swagger to confuse the opponent. Then, keep using Double Team while maintaining Taunt, Hail, and confusion. The goal is to wear down the opponent with hail and confusion damage wihle healing off Substitute damage with the Leftovers. With six Double Team boosts and the 20% boost from Snow Cloak, Froslass's Evasion increases to 90%, and combine that with confusion damage and the opponent has only a 5% chance of landing a move, and even then its damage is limited by Substitute.
Counter: The only counter I can think of is Own Tempo Purugly with Faint Attack. It is immune to confusion, and Faint Attack always hits, for super effective damage too. If Froslass lacks Taunt; Mist, Safeguard, and Defog users can set up on her.