Source: Legacy of the Lost God, pg(s). 80
Iridescent animals are animals subject to a magical process that allows them to glow in the dark and use light-based powers, but diminishes their health and strength, making it all but impossible for them to survive in the wild. Many circuses, menageries and royal courts purchase iridescent animals, finding this effect desirable, but the animal itself never does. Since the process is irreversible, these animals often spend the rest of their lives as showy beasts of burden or objects of ridicule, and many naturalists dedicate their lives to rescuing and fostering iridescent animals. Beasts can also become iridescent, but are never willing to do so and typically do all they can to exact revenge on the person who subjected them to this fate.