Bregalad the Black's huge horndemon is imprisoned in the pentagram

From BatWiki

Description:

The horndemon's was once summoned by Valheru, but never since then. Each Valheru got there Horndemon as a sign of manhood, but that is a time that far far away now forgotten. They are huge and old demon's with with a horn in there forhead. He is rather fat, but you fear him. He is grey-green with a pair of tiny wings on his back.