Board Thread:Spoilers!/@comment-1916997-20171216041419/@comment-1916997-20180307195905

I personally think Dr. Sage being Yzma is the most solid theory so far. The actress has the look to pull off the role, and being cursed as a doctor makes sense to me. Yzma used potions, a doctor uses medicine. Also, Yzma was the advisor/vizier to Kuzco. Generally they are considered to be wise people, similarly to a sage.