I have a couple of Pokemon that I use solely for cheap shots. Persian with Fake Out, Technician, and Life Orb can sometimes take out half of the opponent's HP with the first hit, and they can't hit back. In a double battle, I combo it with Zangoose that knows only Swords Dance and Last Resort.
Also, I haven't used this double-battle strategy because it's too dickish, but it's possible to use Electrode with Choice Band, Hasty, Explosion, and max Attack and Speed EVs to take out everything on the first turn. If your other opener is Ghost-type, it take no damage from the Explosion. You can even have it use a stat-boosting move to become almost unstoppable.
Oh, and in Fallout 3, you can one-shot anything, even a Super Mutant Behemoth, with the right perks and weapon. 100 in Small Guns and Repair, Better Criticals, Ghoul Ecology, Bloody Mess, and the Terrible Shotgun make it literally laughable. I think you can achieve nearly 3000 armour-piercing damage, and the toughest enemies in the game have 2000 health.