Aether

Aether is a divine being who liked to meddle with mortals too much for his own good, as a result they ended up coming in contact with the substance and turned into a slime. They saw this as a punishment from her deity for being too close to mortals and now grieve for their previous life, as now he is stuck in the mortal plane, not allowed to die for eternity. Only occasionally they are able to float as remnants of their divine power remain, their only taste of what it was like, the rest of the time she usually sulks in the corner somewhere. And as a result of having emotions out of reach of typical mortal ranges, their base color is iridescent.