Reaver Ail'zhin casts shadowstep on the MT so be prepared to get ported around and then promply summoned back to your group, training with you all the mobs that you aggro in the process.
This is where you'll find him: Reaver Ail'zhin is in the 2nd temple, "green" level of the map, in the large room in the NE corner of that floor. He spawns somewhat to the back of the room, in the middle