Tyranthraxus

Also known as “The Possessing Spirit” and “The Flamed One”, Tyranthraxus is an extraplanar entity who seeks dominion over all life on Toril. Tyranthraxus can possess any creature that comes near, and can read the minds of those he looks upon. In spirit form, he can hide within magic liquids. It's believed he was able to possess Vorgansharax by concealing himself in a gift of water from the nearby Pool of Radiance.