Nicknamed “The Darkness”, and that being the only name he’s known by (and yes, that’s one of the names I go by on the Internet nowadays…), he is a bat-winged alicorn with a curved horn, and two wildly different personas and forms depending on the type of mood he’s in on that given day.
The lighter colored, blue-eyed pony on the left is when he’s in his normal, sane, unangered state. Also when he’s not in a chaotic mood.
Of recently, though, the pony on the right has been seen more frequently - the ‘other side of the coin’ so to speak - a much more vicious, dark, and chaotic form of the same pony, replete with his own dark thoughts and a penchant for chaotic darkness. Far more likely to get into trouble or at least be more ready to brawl or fight, he’s known to have gotten into a few scuffles, and as such has a more tattered and battle-hardened appearance.
Both of these two are two sides to the same coin - “The Darkness” in light form is still more chaotic and dark than the average pony, but is far more sane and far less dark and chaotic than his darker self.