Black Moblin serve as the Level 3 Moblin type in Breath of the Wild, being stronger than the Red Moblin and the Blue Moblin. They are much more resilient and significantly more health and wield some of the strongest weapons that a Moblin can carry.
These enemies wield some of the widest variety of weapons, including anything from Thunderspears, Flameblades, to even the weakest weapons such as Torches. However, the common weapons that they use include Dragonbone Moblin Clubs, Dragonbone Moblin Spears, Knight's Broadswords, Lizal Forked Boomerangs, and Knight's Bows.
Hyrule Compendium entry of the Black Moblin.