I was playing DooM the other day. A few hours later, I was watching My Little Pony with my sister. Then, an idea rushed to my mind: what would happen if i combined them? Here's my idea.
In a futuristic Equestria, Princess Celestia has started space exploration to find new life. Under the command of her and their newly created Equestria Aerospace Corporation, they launch ships to the space. However, one of these disapears in the middle of nowhere, leaving a corrupted message about death and chaos.
In the rush, Celestia wants to send one of her finest marines to help. However, her best marine is also one of the worst marines her army has ever had. With no time, she convinces him to help on the mission. He accepts. What they find there is nothing good.
Image borrowed from http://anglophobia.deviantart.com/art/Spike-in-DOOM-289879613