Phanter is a Stygian Darkuos from an unknown planet.
He appears as lithe humanoid panther with two tails and stark white fur and icy blue eyes. He wears a basic black loincloth. The Omnitrix symbol is located on his right shoulder.
He has the ability to turn invisible.
He can teleport.
He can create shadow copies in conjunction with his teleportation to avoid attacks.
He has natural claws and teeth.
Not very stealthy without his invisibility unless he's in the Arctic.
His name is a combination of Phantom and Panther.