Succubi and Incubi are described in the Monster Manual as “inhabiting all of the Lower Planes, the lascivious dark-winged fiends can be found in service to devils, demons, night hags, rakshasas, and yugoloths. Asmodeus, ruler of the Nine Hells, uses these fiends to tempt mortals to perform evil acts. The demon lord Graz’zt keeps succubi and incubi as advisers and consorts."