This is one of my first attempts at submitting an exploit in WoW, I'm not entirely sure if it's an exploit, or if it's a repost, I'm tryin to get it on the forum before I forget, I have bad memory.
Requirements: Transforming item (From Halloween IE ghost, skele), And a rogue to duel.
What you do, is send them a duel offer, and when they accept then stealth before the duel actually starts, don't lose them, and turn them into a ghost or somethin right before the duel starts, when I did this, it unstealthed them, and I destroyed him before he even knew what happened.
I know, it's kinda stupid, but it works, I guess.
Edit: I forgot, this only works if the rogue is in your group, so I guess it'd only really work when dueling a friend that's a rogue.