The war between Changelings and Ponies ended in fire and death.
Everypony knew of Celestia's fury. It was her sun that scoured the world, burning anything in its light. It was supposed to kill the Changeling menace, but Celestia just disappeared, leaving the sun too close to Equus.
The sun did not care what it burnt. When the world ended, Ponies sought shelter with the Diamond Dogs. Unfortunately, the Dogs had different ideas.
Dusk Light, a slave to the Diamond Dogs, dreams of revenge. The Dogs betrayed everypony and slaughtered his mother, Twilight Sparkle. Every day, he wishes for the glorious return of Princess Celestia so that he can witness the beasts burn in her fire. However, he's tired of waiting. The hour of judgement is at hand, and he decides that if she won't come by herself, then he will bring her back.
[An entry for The More Most Dangerous Game writing contest]