LOL I once wiped a whole team (3v3) with only an Umbreon, and he's got a Timid nature with full Speed. (Item was King's Rock)
Moves:
- Bite
- Confuse Ray
- Mud Slap
- Moonlight
What I did:
If he's faster, just use Confuse Ray first and keep spamming Bite - half the time the enemy hits itself and the other half it gets stunned by Bite...
If he's slower, Confuse the enemy first and spam Mud Slap, and when my HP is below 50%, use Moonlight to heal.
Oh, and this random one I made was supposed to be for LOL, but I didn't know how well it worked against people who aren't prepared...
Adamant Umbreon with Leftovers, full HP and full Attack EV's.
Moves:
- Curse
- Screech
- Double Edge
- Double Team
You know how it goes: Have him as your leading pokemon, then just spam Double Team until the enemy miss half the time, then use Curse (a couple of times depending on your HP) and Screech (twice enough), Double Edge will be 1HKO against any non-Ghost.
Well that was just a funny idea that flashed through my head so it's 95% unpredictable, lol.