When going down on the last floor of the Cavern of Earth, there you find an orb the same color as the cavern's rotting soil, an evil voice echoes from the orb

"Who speaks to me?"

The orb transforms into an undead with the appearance of a skeleton, a Lich

"I am he who feeds on the power of the earth, I will not be disturbed by mortal man, I am Lich... Fiend of Earth!"