Mascara is not made of bat guano, although that is a very popular false belief that is an urban legend of sorts. The FDA regulates cosmetics and no feces of any kind can be used in cosmetics. There is a substance used in makeup called guanine.
Guanine is in a good deal of makeup and is made using fish scales. It gives makeup a luminous glow or pearly shine. It has been used for many years and is not known to cause any negative side effects. Bat guano could technically be used to make guanine but it is against FDA regulations to use it in makeup.