The Age of Man
Once a natural part of the Feywild, the Fluid were creatures of malleable shape that would be called into form whenever creatures in the physical world looked into reflective surfaces, mimicking their actions back to them through these windows into the Feywild.
Before the fall of the Dragonborn gods, Sin launched an attack upon the Argent Tower, but was unable to defeat its power. Years later Sin returned bearing gifts, and purchased knowledge of the Fluid from Argent. This knowledge, along with an artifact in the form of a glass dagger, allowed the White Dragon to carve out a piece of the Feywild, along with the fluid, into its own realm.
Sin crafted the Fluid over time, giving them thought, will, and a sense of self. She used them as spies who could look upon the world from every reflection in it, and carry world of what occurred their to her. When Sin’s high priest foresaw some great calamity the Fluid were sealed away in stasis, and remained their until the temple was opened by workers outside of Abdera.