The Scourge is invading Dalaran human capital city. There the king's most powerful mages have created magic barriers, which harms the undead. To remove the barriers, Arthas and his lich advisor will have to dispose of 3 archmagies. The first one is to the left before the barrier. Although the barrier harms the undead, it do not destroy them instantly, so they can move inside for a quick blow on the archmagi. Also, along the way, there are those Fountains of Health, which regenerate hit points faster to everyone around it.