"Your soul will be mine!"; "CHAMEK ATH UTHUL ARAK!"; "I SMELL FEEEEAAAAAR!"; "Your resistance is futile!"; "MUHAHAHA".
Behavior:
Demons attack the enemy with extremely powerful attacks until death.
Field Notes:
Demons are the servants of evil. More or less devoted servants of Zathroth, they cause strife and havoc wherever they appear. Their masters are known as Demonlords, Demon Overlords and Archdemons. Long time ago, Demons used to drop Magic Swords and Coconuts. It is said that in one room behind Hero Cave, a Demon can spawn even if there's people inside, but it has not been confirmed. The older "Version" of Demon is Daemon, which was removed in 2000/2001. You can use a Blessed Wooden Stake on a slain Demon to get Demon Dust. In some trickly places like Bazir's throneroom and Oasis Tomb they can have the same behavior and loot as a Goblin (see: Demongoblin).
You need some kind of healing. Do not stand in front of them. They use an attack which look like Energy Beam, but causes Life Drain damage. Kill the Fire Elementals quickly. You can start blocking them at Level 80 with good Skills (blockers with Level lower than 80 will probably die in most of the cases). You can hunt them with a team of Mages using Icicle Runes. It's better to use Boots of Haste instead of Steel Boots because Demons are fast and staying diagonal can be hard. Mages can actually block them with full mana using Magic Shield at lvl 80 with Great Mana Potions while someone shoots (not profitable).
Mages should put on Magma Set, Mastermind Shield and Magic Sword to get more defense. Magic Shield spell is recommended below Level 130. All vocations can use Garlic Necklace to reduce damage from the Life Drain Beam. While you are alone it's recommended to run around and using Icicle runes. If you have Knight in your team he can block few demons and you may use Avalanche runes on them.