Liepard @ Normal Gem
Nature: Timid
Ability: Unburden
252 Spe/ 252 SpA
Fake Out
Foul Play
HP Flying
Swagger/ Grass Knot/ Taunt/ Torment
Prankster usually outclasses Unburden, if your strategy revolves around Swaggery (Swagger + Trickery). And at that point, you're better off using a Prankster like Sableye or Murkrow, who have more bulk and recovery.
The "mixed" idea is pretty good, but Liepard doesn't really have the movepool to properly use it from what I can see. The great thing about Prankster + Foul Play is that it means your Pokemon has Attack and Speed basically covered, so you can invest in Defense. With a frail pokemon like Liepard, it's not the best user, though it does have Thunder Wave and Encore.