Knight of Cerebus

Dragondawn:
* The game has two. The first being Hordun, who committed a particularly despicable murder, the other being the three Dragons of the Apocalypse, who turned the semi-comedic court game into a fight for survival and the fate of the whole world.
The Stone of Power:
* The dragon from the second is a darker villain than the first one. While the first is just a power-hungry wizard, the dragon is an Omnicidal Maniac willing to restart the mass murder he did 500 years ago.
Satan Saga:
* While not exactly light-hearted, the first arc is pretty peaceful until Trianuk enters the plot. It then features the first betrayal and personal murder. Since then, prenty of psychopathic and/or ruthless villains make an appearance and characters from both sides get killed and even some villages wiped out.