He is located on the roof part of the area. When Bonfire Intensity is 2, there will be two of them.
Avelyn (one per hand)
Black Witch Domino Mask (very rare)
Spawns only once per playthrough. He will respawn if a Bonfire Ascetic is used on the Belfry Sol bonfire in Belfry Sol.
Oddly enough, he never performs any power-stance Avelyn attack.