It's the DEMOGORGON!

You enter a dark room, covered in cobwebs and shallow puddles. You search for a light when you hear a faint hissing and footsteps growing louder. You ready your sword and put out a lantern to see what horror awaits you. It's...it's... it's the Demogorgon! The beast of two heads stalks closer to you, fangs flashing and tentacles stretching forward, as you prepare yourself for combat. Best of luck, traveller!