The greatest threat to spelljammers, and indeed to every living creature in the Pyrax System, is the collection of aberrant monstrosities collectively referred to as the Scourge of the Stars. The largest groups within the Scourge are the Illithiad and the Host Abolethic, but at the apex of the Scourge sits one powerful being: Mak Thuum Ngatha, the Nine-Tongued Worm. Little is known of this creature, but that it is revered as a deity by the mind flayers and the aboleths. It believed to reside on the surface of the alien planet Atropus, but often roams the solar system inside a massive meteoric vessel, attended by aboleths, mind flayers, and many other aberrant creatures.
Note: This monster stat block borrows powers from Vecna, who does not exist in the Pyrax System.