Just noticed this thread has been kinda dead, so since my new team has a few dark horses I thought I'd revive it:
Pokemon Showdown! Username: soulswag
Prior Hall of Fame Standing: 1857 rank with Shedinja -- currently 1892 with my new dark horse team
Current Dark Horse Pokemon: Tornadus-T (1.56711%), Mew (2.88408%), Rhyperior (0.51656%)
Explanation of Dark Horse(s)
Tornadus-Therian (M) @ Assault Vest
Ability: Regenerator
EVs: 248 HP / 4 SpA / 252 Spe
Hasty Nature
- Hurricane / Aerial Ace
- Knock Off
- Superpower
- U-turn
Just a great pivot. Having something so ridiculously fast on a stall team is awesome. He can really save your ass vs. the Latis and stall-breaker Gengar. Even without investment, hurricane hits physical walls and M-Venu pretty hard and means you can go for the surprise kill after they've been worn down. Aerial ace is specifically for countering CM Keldeo, which can be necessary if you lack a mega Venusaur. HP EVs can be changed for SpD EVs, attack EVs, or even SpAtk EVs depending on your preference and play style.
Mew @ Leftovers
Ability: Synchronize
EVs: 244 HP / 248 Def / 16 Spe
Impish Nature
- Knock Off
- Will-O-Wisp
- Defog
- Roost
Great defogger and general physical wall. Can switch in on virtually every physical attacker and burn it before it does anything too harmful, then roost off the damage. Only Lum/SD Garchomp and Excadrill as well as fast Mega Hera really scare this guy. EVs are to outrun adamant Bisharp and burn before he gets in the knock off:
-2 252+ Atk Life Orb Bisharp Knock Off (97.5 BP) vs. 252 HP / 252+ Def Mew: 159-190 (39.3 - 47%) -- guaranteed 3HKO after Leftovers recovery
After the burn you can just roost stall non-SD variants out. Make sure to get something else for SD variants. Shouldn't be hard to do after a burn.
Rhyperior @ Leftovers
Ability: Solid Rock
EVs: 252 HP / 100 Atk / 156 Def
Adamant Nature
- Earthquake
- Rock Slide
- Stealth Rock
- Dragon Tail
Rhyperior covers Mew's major weakness to MegaZard X. This is as close to a hard counter as you can get. WoW variants are annoying, but you can still set up rocks in his face while he does little to you in return. EVs let you out damage 252/252+ Chansey's soft-boiled after a knock off (not hard to get with this team). In general, Rhyperior has a lot of flaws and is only on this team for specific support needs. Would not recommend for most teams.