Toth-Amon

Toth-Amon was a powerful wizard who resided in the Crystal Palace where he guarded the mystical Heart of Arhriman. He kidnapped Jehnna so as to use her to obtain Dagoth's horn and use it to resurrect the dark god himself. When Conan's party came searching for Jehnna as well as the Heart of Arhriman, Toth-Amon trapped the Cimmerian in a mirrored room where he transformed into an apelike monster and fought Conan.

In this form, Toth-Amon was invulnerable to Conan's physical attacks however Conan weakened him by breaking all of the mirrors, revealing the "ape creature" was only an illusion (it crumbled into broken glass). The real Toth-Amon was hidden behind an unbroken mirror, and Conan flung his sword through the glass, impaling him with it. Undaunted, the dying wizard entered the room and killed himself by touching the Heart of Arhriman which caused his body to crystallize and disappear.