Darkmantle

. , and the monster attaches to the target. If the target is a Medium or smaller creature and the monster had Advantage on the attack roll, it covers the target, which has the Blinded condition and is suffocating{suffocating} while the monster is attached in this way.
While attached to a target, the monster can attack only the target but has Advantage on its attack rolls. Its Speed becomes 0, it can't benefit from any bonus to its Speed, and it moves with the target.
A creature can take an action to try to detach the monster from itself, doing so with a successful . On its turn, the monster can detach itself by using 5 feet of movement.

Magical Darkness fills a -foot Emanation originating from the monster. This effect lasts while the monster maintains Concentration on it, up to minutes. Darkvision can't penetrate this area, and no light can illuminate it.