Although the skill {Death Wave} would not heal the caster himself, it could be used to heal others. Hence, if two Spectre Wizard were to stand side by side, they could technically heal each other endlessly, making the battle much harder. If he kites too many of them at the same time, it would be really difficult. Stack them up to a certain amount, all the monsters could basically heal themselves back to full health if Zhang Yang is unable to kill them all in a blast!
What a sad case indeed. Zhang Yang had initially thought that he could at least perform a fast mass-kill since the tower floor was crowded and small. Sadly, due to the AoE healing {Death Wave}, Zhang Yang had to change his killing style to one at a time! The slowest, boring-est, lamest style ever!