Black demons are large demons that inhabit a few dungeons throughout Gielinor. As demons, they have high combat stats but rather low Defence for their level. They are weak to demonbane weapons; as with most demons, they are also weak to magical attacks.
A unique black demon is defeated during The Grand Tree. This demon can be re-fought in the Nightmare Zone after the quest has been completed. Killing Black demons in Nightmare Zone will count as a kill for a Slayer task.
Demonic gorillas, Balfrug Kreeyath, Skotizo, Porazdir, and Kolodion's final form can also be killed in place of black demons in regards to a Slayer task.
Black demons can be safespotted with Magic, Ranged or Halberds in all of their locations.
Black Demons have no slayer level required but they do require 80 combat to be assigned.
I’m going to be honest here, if you get assigned Black Demons at level 80 combat, you are going to have a tough time.
Black demons have high defensive stats making them a very long task but they also hit quite high with a max hit of 16.
For this reason, Black Demons are a recommended BLOCK task for anyone training slayer under 100 combat.
You can be assigned Black Demons by Chaeldar, Nieve, Konar, Krystilia and Duradel.
Black Demons hit very high, for this reason, you should always pray melee against them.
Don’t bring tank gear on this task, instead bring proselyte and other prayer boosting gear.
If you have the money, bring a cannon as well and camp them either at Taverley Dungeon or Chasm of Fire.
Weaponry-wise, you are best off using the Arclight on Black Demons. However, using them on Black Demons would be considered a waste as these charges are much better spend at Abyssal Demons or Demonic Gorillas.
At Black Demons, simply bring prayer boosting gear as you will be camping the melee overhead.
As for your weapon, just bring your highest DPS weapon.
Black Demon tasks are slow (unless you have a cannon/arclight) and the drops are simply not worth the effort.
However, there are plenty of monsters that you can kill INSTEAD of Black Demons WHILE on a Black Demon Task.
Here are the worthy Candidates:
Players with completion of Monkey Madness 2 should always go to Demonic Gorillas over Black Demons for their juicy 1/300 drop rate of Zenyte Shards.