Another unsuspectable goat in randoms is volbeat, he locks you on a setup move with prankster encore, paralyzes you with thunder wave and tgen u turns to your sweeper, I won lots of battles with him
Any mon with sub seed are incredibly frustrating to play against, mostly Tropius of course. Salazzle is another annoying mon to deal with, it's too fast plus it can work together with smart switches to ko one or two of your mons. But IMO the king/queen of randbats is the almighty moon fish of pokemon Alomomola. You can win any match if you play Alomomola well and if the enemy don't have a good counter to it switching in and out.