(I am rewriting this fic into something better out of my image. I think it may take a while, but I have enough inspiration and value time to actually remake such dread into good and readable dread. Even when there can't be any kind of good dread, you know what I mean. I thank you for reading and remember, I am only an Entertainer of literature, just like you.)
Deja Vu, believed to be a dead alicorn, confronts his two siblings in blind anger and jealousy, steals the Elements of Harmony and threatens to cast judgment upon the world that has forgotten his existence as the Alicorn of Time.
Sending the Mane six to retrieve the artifacts and stop their brother, Celestia and Luna seek knowledge to understand their brother more, and decipher why his disappearance was not noticed to be fraud as well as his death.
Will the Mane Six stop him in time and will Celestia and Luna finally solve the clue, and will Pinkie Pie gain her vengeance for her Sand Castle? (I'm just being silly on the Sand Castle...maybe.) It's up for you to find out and them to solve.