There was a random forest ranger in the Moor of Icirrus in Black and White 2, whose only Pokemon was an Emolga with Double Team and Discharge. I had six Pokemon with me (one was an HM slave Sunkern though, so it doesn't count). I managed to hit Emolga once (first attack missed), but after that he boosted all the way to +6 in my face, and then swept my entire team with Discharge. Discharge was not anymore than a 2HKO on any of my Pokemon, but after he got up two Double Teams, I didn't hit him a single time.
Christ, I was mad.