
Given that Halas kept a large platinum plate bolted over the dreadnought's eye, this astral dreadnought likely has the same ability as in Mordenkainen's Tome of Foes: creating an antimagic cone. Demiplanar Donjon: The Mighty Nein entered the dreadnought's mouth to find a demiplane that Halas had used. Halas Lutagran kept this astral dreadnought chained and blinded, with a lever controlling the opening and closing of its mouth, so that he could use the capacious demiplane within as a ritual chamber.
Its face had a single eye with a horned brow and a 12-foot-wide mouth edged with hundreds of two-foot-long teeth. Its body was covered in spiky armored plates and hardened, veiny, pale flesh plates.
It was shaped like a bulbous, muscular serpent with two thick arms ending in pincers. This astral dreadnought was 20 to 25 feet on a side, though its silvery tail seemed to curl off into an impossible distance.