Gen 4/Gen 5
Damn this thing is versatile, here's mine:
Clefable (M) @ Toxic Orb
Ability: Magic Guard
EVs: 216 HP / 44 Atk / 192 Def / 56 SpD
- Fire Punch / Fling
- Cosmic Power
As I said, this ugly thing can be played a number of ways, I prefer to facade staller. Toxic Orb + Facade is good on things like Swellow, or Staraptor, but Clefable gives it a new face. What Clefable does differently is it takes no T-Orb damage with the Magic Guard ability, so it can't be affected by other status afflictions that would hinder it, i.e. Burn, Paralysis, Sleep, without taking residual damage. Facade is boosted by the stat affliction, and STAB, it is the main offensive strategy.
Fire Punch covers steel types that facade won't hurt. Fling can also be used in this slot, as it will badly poison anything it hits, but only once. Soft-Boiled is for recovery, and Cosmic Power makes the set by making Clefable nigh impossible to take down without a miraculous crit.
This thing can't be afflicted with status, it can't be simple swept, and it heals off damage, unless you crit, this thing will be around a while. EVs are fairly simple, HP for bulk, Atk just to put it over 200, Facade hurts even with Atk low, and enough in each defense to equal them out at 230, 345 each after a single Cosmic Power.
All the sets given so far have been really cool, and I'll try a couple for sure, this is just my two cents, hope it helps.