Strid

The Strid were a species of sentient, gelatinous body-snatchers. They were enemies of many powerful species in the universe and even beyond, but survived for an unusually long time due to their patience, keen sense of observation, and ability to retreat when they knew they were outmatched.

Nature
Their natural form was a blue ooze; if they did not constantly steal new humanoid bodies, they were unable to maintain a coherent shape for more than a few hours, after which they would revert to a formless liquid. They couldn't speak when in a possessed body, for fear of being exposed as some of their ooze leaked out of the open mouth. Keenly aware of their limitations, the Strid were noted for their amorality but also their patience, being content to watch and observe for centuries on end, waiting for the right time to make a bid to gain more power. Strid were present, watching silently in the background, at most major events involving powerful species of their universe, from humanity to its very rulers. They "seem[ed] aware that the great figures they seek to fight have an inevitable draw towards victory, something scorched into the nature of their world"; as such they were much quicker to act when interacting with visitors from other universes, which they did reasonably often, such that they were known even to the Firmament, a powerful species who ruled a set of parallel universes far beyond the Totality and who did not like to interact with the Totality. (PROSE: Rachel Survived)

History
The Strid were slowly moving forward with an invasion of the Earth in the early 21st century when they became aware that agents from the 10,000 Dawns, including the Arbiter of Knives of the Firmament, two spies from the Great Assimilation, and two agents of Dawn had made their way to New York City seeking the Book of Books. Though they failed to capture Rachel Edwards, whose temporal shadow the interlopers were using to cloak themselves, the Strid were able to turn the situation to their advantage by getting to the Book of Books before anyone. With the Arbiter of Knives having taken out agents of the local powers, the Strid decided to auction the Book of Books to either of the three powers from the 10,000 Dawns.

The Firmament offered them a planet, the Assimilation offered them that and a seat at the Council of the Great Assimilation, while Dawn refused to negotiate with the murderous beings and simply gave them an ultimatum to surrender their prize peacefully. In the end, however, Rachel rendered this moot by threatening (as a bluff) to kill herself, which would allow all the alien powers' presence to be noticed by the rulers of this universe. The Strid accepted their defeat quietly, handing over the book, and retreated. The usual silent, disguised Strid agents were later seen watching as the Book was transported out of the Public Library to a secret location by human authorities. (PROSE: Rachel Survived)