Ever heard of a strategy that has been said to be a gimmick, but have discovered that if you don't have the right Pokemon for it, it can be incredibly difficult to get past? This is what I have faced countless times on random matchup. Since there's no restrictions, like evasion and sleep clause, people take advantage of it, and use incredibly annoying Pokemon. The biggest example of this I have ever faced is a Prankster Liepard with Substitute, Assist, Swagger, and Foul Play, and it held leftovers. On the first turn, it used assist, and the random move it chose was Spore. it then set up substitute, and kept using Swagger, then used Foul Play to wear my Pokemon down. When my Pokemon woke up and used a move to break the Sub, it would use assist again. At this point, I was thinking the the other two Pokemon he chose must only know Spore. I lost that match due to that strategy.
So what Pokemon have you faced that annoyed the heck out of you?