Mad Mage

His true name is Boyd and he is Lloyd's brother.

Official Creature Artwork

His attacks are a bit similar to a Fire Elemental's and Thornfire Wolf's, but a bit stronger.

Treat him like a weak Infernalist. Also, he strongly targets lower level players. However, in some worlds it's hard to deal the most damage because a lot of players are waiting for him during the last waves of attacks.
Paladins: This creature is weak against physical damage so Assassin Stars combined with the Sharpshooter spell should defeat him fairly rapidly.
Knights: Like paladins, it's recommended to use strong physical spells such as a combination of Blood Rage and Fierce Berserk.
Mages: Should use Sudden Death runes. If you are a Druid, you may use Eternal Winter to deal a lot of damage.
However, if you are alone with the Mage and you won't waste supplies, you may attack him like a common creature.

After the first part of the Summer Update 2013 the World Change called Their Master's Voice was revised multiple times. Because the scripting of the Mad Mage became complicated which led to bugs, Cip decided to remove the Mad Mage from Tibia for some time, to reprogram the scripting of the Mad Mage correctly. See Mirade's post on this topic.

The roleplaying consequence of this issue was the (temporarily) implementation of the NPC Sane Mage, the sane version of the Mad Mage. During this time, Guide NPCs would say "The strange tower with the servants on Edron currently seems to be completely impassable because of a severe slime outbreak." instead of their usual answer, when asked about Master's Voice.