I once started writing a story with a "monster universe" setting but in space. Werewolves and vampires always at war with each other. Humans and animal-humanoids caught in the middle. A few eldritch horrors lurking around the void.
I did a self contained short story set in that universe, about an observation station sitting at the edge of the galaxy, monitoring for potential intergalactic information. They detect a large mass of dark matter that only became detectable when it got close enough to reflect light from our galaxy. As they observed, they realized that the string of dark matter was just a tentacle the size of a large star cluster, and they couldn't see what was on the other end. It swept close and then retracted away.