Their Master's Voice World Change/Spoiler

Go to Edron, here. You can ask the NPC Servant Sentry about his master (the mad mage).

The dungeon may be filled with the mad mage's servants. They come in waves of Iron Servants, Golden Servants, then Diamond Servants. They might carry some Slime Mould which is needed for the Elementalist Outfit. Killing all servants will provoke their master to show himself and you will be able to fight him. However, if all servants are dead, a dangerous slime fungus will slowly start to spread in the tower and can only be removed with the help of the Slime Gobbler. The servants and the mad mage will only reappear if all the slime fungus is gone.