Elder Brain Dragon. The elder brain augments the already fearsome qualities of its draconic host with its own psychic abilities, as well as a grappling tentacle attack and the ability to, ugh, vomit a stream of illithid tadpoles that burrow into your flesh, dealing psychic damage. Sponsored by hit point press' animated spell cards:
Brainstealer dragons are the monstrous hybrid between an illithid and a dragon, which is likely the result of a mind flayer ejecting a tadpole into the mind of a captured dragon and transforming it through ceremorphosis. The elder brain is a huge, fibrous mass of cognizant brain tissue covered with writhing feelers. They bare no resemblance to the illithid monster.