Slash... The swordsman at the front killed the last mutant from the wave. With that mutant died, the boss howled painfully. After that last mutant was dead, the boss got some damage and died.
"Okay, we are done!" The glasses merchant said while picking up the boss' loot.
With the boss died, the party had finished their dungeon. It took long enough than normal dungeon run since they did it on purpose. Usually, a normal run would keep one mutant from the first wave alive. Then, they would attack the boss until he died.
However, this party didn't do this strategy. They wiped out waves after wave and let the boss took the damage because of the clearance of the mobs.
Every wave cleared, the boss would suffer fixed damage. His health would be reduced by 5% every wave cleared. This means there were only at most 20 waves, and each wave would consist of 8 monsters. In total, the party had removed 160 of the boss's mutant guards.