(Based on the group photo made by KFscorpion and I give him creds for the cover)

The mane six and the Princesses are up against someone who has been enemies with the princesses for as long as they can remember: The Gatekeeper of Hell, The Leader of the Cenobites, Pinhead and he's brought an army of the best he could find to take over Equestria. Celestia, Luna and the elements gather themselves their own army and plan to fight against this threat.