Humans are a very consistent sapient in the various universes. As a result, Eaters are creatures that prey on one of the most consistent forms of energy: human potential, whether it is psychic, magical, or physical. Eaters vary widely, depending on their home universe and the availability of human victims.

Varies widely, though most are close to human skin colors

Human magic/potential

Physical class - consumes human life force through some kind of physical human product. Includes vampires, flesh eaters, and -cubi.
Psychic class - feeds on human willpower by tricking, corrupting, or controlling humans. Includes fair folk, sirens, and demons.
Divine class - the only type of Eater who can digest human awe, the most powerful and renewable source of their magical power. Awe can be both fear and praise, both of which become ambrosia when given ritually. Eaters of this class are typically worshiped as gods.