I dont know if this is a repost but probably not, me and a friend found it while tanking our mmr.
Basically what you do is when the game is about to start and you have dalaran sewers you can blink against the water that pushes you out and stay up above, but you have to be quick on the trigger finger though. Be aware it will pop again when the other team reaches a certain point in the arena you may need to get ready iceblock or blink again if its up. Most the time you can stay up there for the whole match ~30 minutes.
This is useful for mage mage. 2v2.
Sorry I don't have screen shots but a mage could confirm this very easily.