Lucubra

Lucubra are from another dimension, It has a green and gray gelatinous body with red teeth like markings in its body, resembling some kind of lizard. It uses tentacles to feed on its victim's thoughts and uses them to communicate with others, once a person has been fed upon the Lucubra can send them commands telepathically. They seem to range in sizes, one being as large as a dog, while another was twice as big as a man.

Lucubra has the ability to feed on the thoughts of humans and possibly other species. It is stated that it feeds on the part of the mind used to pray or meditate until there is nothing left of the victim's mind. The victim then becomes it's obedient servant, evident by the turquoise eyes, which it is implied it can control from other dimensions. Lucubra is also very durable, able to withstand repeated attacks, while taking little to no bodily damage. it can fire a powerful laser beam from its face and climb walls.

Trivia

 * According to Gwen Tennyson, the Lucubra is a demon from another dimension sealed by Sir George using a spell.