Generic Doomsday Villain

4 vs. Satan:
*The Master of Darkness, who appears out of nowhere and serves as the villain for the final dungeon.
Alex in Princess Quest:
*NONE
The Stone of Power:
*NONE
The Three Kingdoms
*NONE
Dragondawn
*NONE
Harter Knall
*NONE
Hero Story
*NONE
Kill the Demons
*Rustoc, who appears at the last second. While Casper is an arrogant guy with a god complex, no motive is given for his partner-in-crime.
Satan Saga
*NONE
Story of Hero:
*NONE
The Legend of Devils
*NONE
The Sidestory Duology:
*The demon created by Rudolf has no personality other than being a destroyer.
The Time Of Bloody Fear:
*NONE