A group of a mage and a priest is the ideal way for this wow powerleveling strategy to work. Once mage gets instant arcane explosion then it is off to the races by killing groups of monsters slightly lower level than the mage/priest and be able to kill 10-20 of the mobs at once using AOE spells from the mage and the priest's flash heal spell but can also do it without the flash heal spell to some degree. This wow powerleveling strategy has been tested by many people and myself so it absolutely works great!

 

If the priest is getting hit you are both dead since his heals will be interrupted. Make sure you move around to keep aggro on all monsters. Frost nova will also prevent mobs from running when they get low hp. Pretty much any build will do, just make sure that you have improved arcane explosion. If you go frost make sure to get improved crit % of cone of cold as well as lower the cooldown on frost nova. If you go fire then combustion is nice for that initial bang.

 

On the down side this wow powerleveling strategy only works with mages and priests. Use frost nova to root monsters so that you can AOE them without getting damaged as much. Also remember that you can combo frost nova with cone of cold for some massive damage if you are frost specced! Finally, a mage can do this himself without a priest but it is much less efficient. Typically a mage can only do this to 3-5 monsters at a time maximum because of their low hp and no healing abilities. If you do the math, 5/1 is less than 20/2 so by duoing with a priest you are actually increasing your own profits!