Altaïr Ibn-La'Ahad, Mentor Assassin of Masyaf, having sealed himself away in his library, The Apple hidden, waited in his library for death. The Apple seemed to disagree with this. After a bright light emanating from where The Apple resides blinded Altaïr, he awakens in a grassy meadow, with all of his equipment, his robe... and four legs.

Arc 1:Altaïr's Arrival - Altaïr is sent to Equestria in a flash of bright light. There, he learns of impending war between the changelings and ponies. In order to assist them, Altaïr establishes a new Brotherhood.
Arc 2: The Resistance, The Rebellion - With Altaïr captured and the Brotherhood destroyed at the hands of the undercover changeling, Deception, it's up to Ezio and Rainbow Dash to defeat the changelings. Meanwhile, unrest grows in the changeling hive.
Arc 3: Lost to Time