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https://www.youtube.com/watch?v=lAJaRUfDkNY (I suggest 1080p to see anything)
If you can't tell from the video, the NPC Anduin follows you around this zone during a quest and attacks anything that attacks you - including players!
Futhermore, if you're a rogue and vanish (or druid, mage, whoever else), Anduin continues to fight your opponent, while you watch!
The only drawback is the other guy can get out of combat and fly away, otherwise this would've been the perfect way to annoy level 90s fishing in this area (i'm not max level yet, otherwise I'd just gank them).