This just gives a general idea of how Tarmar is supposed to look. Tarmar is a tar demon, and can potentially shift into the form of a winged imp or any other demonic form. The head doesn't change form, and the gem serves a mysterious purpose I won't reveal here.

Tarmar is really stretchy and clingy but inescapably sticky.

The Tar Detail is just meant to show that Tarmar is really gooey looking.

Tarmar, Lord of the Deep Pits is a tar demon bearing glowing red eyes and a tarry body and head. His imp form resembles an imp with large arms and feet and gooey wings. His head bears tarry horns, one set of horns pointing up bearing a mysterious soul gem and the other two sets pointing away from the direction he is looking at. The mysterious octahedral gem emits an eerie soul fire, and that's all I can tell you.