Black demon (The Grand Tree)

A black demon is summoned by Glough as the boss of The Grand Tree quest. The demon is very strong and can hit over 1000 using melee attacks, so Protect from Melee is recommended to ward off some damage from its attacks. Unlike black demons everywhere else in Gielinor, this demon cannot use Magic and is weak to water spells, instead of bolts. Hiding behind the rocks directly south or going down the tunnel slightly will prevent the demon from using melee attacks and allow you to defeat it without taking much damage of your own.

If you take too long to fight the demon or go too far down the tunnel, it will disappear into thin air and you'll have to start the battle all over again. This is a great way to quickly escape without teleporting (but be mindful of level 44 bats).