Hey there! Klefki can be a bringer of destruction if you use it right! With prankster, a great typing, and access to moves like thunder wave and foul play it can make a great supporting 'mon.
If you wanna try it out this is the set I used in VGC '15 a while ago. It didnt go to well, because it doesnt fit the VGC meta game that well, but its great in OU, so if you wanna try it, try using this set:
Klefki @ Light Clay
Ability: Prankster
EVs: 252 HP / 64 Def / 192 SpD
Bold Nature
- Light Screen
- Reflect
- Thunder Wave
- Foul Play
Or this one if you want to use it a bit more annoyingly:
Klefki @ Leftovers
Ability: Prankster
EVs: 252 HP / 4 Def / 252 SpD
Careful Nature
- Swagger
- Thunder Wave
- Foul Play
- Toxic