A Destiny crossover.

The Warlock, Crux-18, must figure out where he is, how he got there and how to stop the Vex from encroaching upon the world of Equestria. Naturally he's going to need to make some new friends.
But it won't be easy, the alliance between the tribes is still relatively new and tensions are high.

This story takes place a few generations after the unification of the three tribes. This mean's no Celestia and Luna. (provided my info on MLP Lore is correct)