That can defeat Archon, the ancient black dragon that has ruled Equestria for over 500 years.

This story is taken place in an alternate universe in which the mane six have since died. Twilight Sparkle gave her life with a powerful spell that put to sleep a black dragon named Archon for 10,000 years. 1,000 years after Twilight Sparkles death Archon suddenly awakes and wishes to wreck havoc and claim Equestria as his own. 500 Years after the siege of Canterlot and the overthrow of Celestia, a young mare named Sedgwick discovers an ancient magic hidden by Celestia that can be used to destroy Archon.