Thread:Trevor7626/@comment-25512318-20170301170753

He starts in a Predalien form, but later transforms into an Alicorn. He is introduced as the main antagonist of  The Rise of Midnight, but then becomes the secondary protagonist to help Twilight defeat the  true main antagonist.

The Rise of Midnight
12,000 years ago, the spirit of Equestria created Midnight (also known as the Black Twilight Sparkle). Midnight was created to destroy all villains attempting to conquer Equestriaa. Midnight began to do his job well beyond his purpose and Princess Twilight Sparkle was forced to intervene. There was a huge battle between Princess Twilight and Midnight. When Twilight finally won, Midnight was laid to rest in the Frozen North. Unlike his benevolent twin Princess Twilight, Midnight sees all equines as a blight on Equestria, and won't stop until they're all removed from the planet. It's because of this that Midnight came into conflict with Twilight.

Thousands of years later, Midnight was awoken by a meteorite. Midnight went to the Crystal Empire and burrowed, reappearing and attacking the Crystal Empire. The Crystal Guards fought Midnight but were no match and Midnight left as he burrowed again. Midnight appeared in the waters off the archipelago of the ocean, where Tirek and Princess Twilight Sparkle were battling. Midnight flung Twilight aside and engaged Tirek. The two battled down to the sea floor in the trench, where a volcanic eruption supposedly killed them. But Midnight and Tirek lived on, appearing near Mount Everhoof, with Tirek exiting an erupting volcano and Midnight emerging from the ocean's depths. Upon metamorphosing from his Predalien form to Alicorn form, he flew to Canterlot to exact his revenge on Princess Twilight. The sinister Alicorn seemed to have the upper hand against his less violent counterpart, but soon, in the heat of the battle, Tirek appeared. Princess Twilight and Midnight teamed up to combat Tirek together in defense of both Equestria and the equines. Once Tirek was defeated, Midnight and Twilight carried him out to sea and dropped him in the ocean and created a seal that permanently keep him lock up.  
 * Unlike the Equines, he stays in his Predalien form every time he travels from the Equine world to the human world.