Omnicidal Maniac

4 vs. Satan:
*Satan. It's implied after he becomes God and fills the world with demons he'll use his position to destroy the entire world.
Alex in Princess Quest:
*NONE
The Stone of Power:
*The dragon from the second part.
The Three Kingdoms
*NONE
Dragondawn
*The appropriately named Three Dragons of the Apocalypse seek to the destroy the world, as apparently it's the reason they exist.
Harter Knall
*NONE
Hero Story
*NONE
Kill the Demons
*NONE
Satan Saga
*Trianuk seeks to wipe out everyone in his world to avenge his wife.
*Satan, who made Trianuk the genocidal maniac in the first place. Downplayed, as he still plans him and his followers to survive Trianuk's attack.
Story of Hero:
*The Grimoire plans to burn down the entire world.
The Legend of Devils
*Satan. Apparently he has plans to kill at least hundreds in order to "balance" his godhood in addition to having hundreds killed.
The Sidestory Duology:
*Rudolf Hitler has people driven insane, fully intending that they'd wipe out each other.
The Time Of Bloody Fear:
*NONE