Since the Mercenary leader attacks only with magic and summons Forgotten mages more frequently than warriors or rangers, players should use Protect from magic, wear melee armour, and attack the Mercenary leader first. Once the Mercenary leader is dead, the other summoned mages, warriors and rangers will eventually teleport out and disappear, so it is suggested to wait outside the room for this to happen, unless the leader is of a very low level.