After Starswirl the Bearded presents Twilight with a magical artifact, the Main 6 test its abilities with dire consequences. Nearly struck dead, Fluttershy finds her nights swallowed by nightmares of war and death on a scale that breaks the mind.

It is quickly realized that this artifact was not just content with lashing out at Fluttershy. And as each night goes by with no way of stopping its malicious influence, the entirety of Equestira is at risk of loosing themselves to the bloody nightmares.

(A Crossover of MLP and Warhammer 40k)