The Dark Below

Light without darkness is blinding, and dark without light is an abyss; one cannot exist in meaning without the other.  

There is a school of thought that the followers of Morgath have formed a broken reflection of the Valar and Maiar - for every good and positive that the Valar pose, the fallen have taken and twisted it. For instance, where Yavanaa brings growth and birth, her fallen counterpart would twist it, and make it something else; maybe cancer, pestilence, or infection.