Dark Vessels are demons. This type of monster is likely called a Vessel, and the "Dark" prefix to their name denotes a particular type.

These human mages are commonly found standing motionless, amidst various other types of Dark enemies. Vessels are harmless in their human form, but become very dangerous melee fighters if they manage to pull a demonic entity into themselves. In that form they are known as Activated Vessels, and are ferocious fighters.

Dark Vessels look a bit like Dark Cultists, but Vessels lean on tall crooks, and remain motionless until they transform, while Cultists are mage-like enemies who cast a variety of spells and summon demons.

Media

See screenshots and concept art of the Vessel in the Image Gallery.

Vessels in their usual incantation circle, with one activated.