Life is hard for Applejack, because she's a farm pony, because she's an earth pony, but mostly because her body is composed of enigmatic and mysterious dark matter. Some days in particular are just not good for a super-heavy pony with her own gravitational pull.

(Cover image by KYMSnowman. Based on this video by beatledude64. Some A lot of artistic liberty was taken in the actual physics behind this story for the sake of comedy.)

Luna is no longer Nightmare Moon, and has returned to rule Equestira once again, but not everypony is so ready to forgive. When a secret organization kidnaps the Elements of Harmony and threatens to murder Luna, Rainbow Dash must go back into the memories of her ancestor Firefly, to learn the ways of the Assassins to fight this new terror and save the new princess, as well as her friends.

Credit to he4rtofcourage for the title image.