I use to have a friend who was an enormous troll. Thing is, he was extremely clever. He would come up with (and I imagine he still does this) the most unthinkable, insane, annoying and effective way to do well in competitive play. The most annoying thing he's ever made me face would have to be the following Smeargle:
Smeargle @ focus sash
Trait: Own Tempo
You know the strategy. First use Trick Room, while receiving an attack and dropping to 1 HP in the meantime. Then use spore to incapacitate the enemy, followed by endeavor and dragon rage, which in that order kills the opposing pokemon. He wiped out half my team, so of course I couldn't mount a comeback.
I have claimed Alduin, the mighty dragon! He shall one day return to bring forth the end of time, and fulfill the prophecy of the world eater.