Here is a little tip for arenas when trying to find out what those stealthed classes are. It may be obvious to some, but I have been getting more serious into arena and some people still don't know this, but say you are doing 2v2, and a priest shows, but you can't find another class. If you click the priest, you can see his buffs, if they aren't buffs from himself, you an tell which class buffed him, so it can give you and edge sometimes.
For example, you are fighting a Warlock and a _____, but you see that the warlock has Arcane Intellect, you know the mage is invis.