I'm facing the rather daunting task of writing a millennia-old foe for my Paxverse characters that is supposed to encompass everything sentience fears, "a vast, incomprehensible darkness, uncaring of ships or weapons, bent only on devouring everything it touched," something that originated on another world even further back than the mythos of the Paxverse goes (about ten thousand years), that basically swallowed an entire empire and almost consumed a few others. I want it to be universally scary, though, so I need some information: tell me what scares you. It doesn't have to be specific; generalities will do. But it should be the most basic thing you can think of, as unreasonable as possible. Fire away.