Misty sucks. I have a 31 misty that I tried in pvp for a while. You activate the arcane and lots of the debuffs are removed but then reapplied from the opponent's pets.

I charge heal, get stunned out of heal, use misty. Now I have to recharge heal and right before I heal I might be dead.

There are other pets that offer more than 300hp as well.

Don't rely on misty.