Like the other 3 Plutonian moons plus Charonball, it is thought that he formed from a collision between Plutoball and another dwarf planet billions of years ago. Thus, he likely is a mixture of water-ice, silicates, and frozen gasses.
Orbit - Rotation
Kerberos has a nearly circular orbit, in which he completes every 32.1 days. He rotates chaotically, meaning he doesn't have a stable rotational period nor obliquity (axial tilt). He is one of the 4 discovered chaotically rotating moons.