Kastor and Pallux are one of the earliest bosses in the Forgotten Revolt story arc in Kingdom Hearts: Blooms of Chaos. Rather than fighting the Unversed by themselves, you must face Kastor and Pallux's flying machine. This battle takes place in the middle of a Metropolian body of water outside the Timeless City, with a large circle of water frozen around you to serve as the arena.
Spoilers end here
Shockwave: The flying machine slams its hull into the center of the arena, sending out green shockwaves that you must leap over to avoid.
Twist of Shadow: Kastor takes the helm of the machine and begins to spin the device rapidly. A tornado of darkness will appear below them, sucking you towards it. You must dodge roll or glide away to escape the vortex.
Ultraviolet: Pallux takes the controls and begins to rapidly press buttons. A strange cylindric device will come out of the middle of the hull. This device will begin radiating with the energy of light, and then a yellow target will appear on the ice below your character. A beam of light will shoot out of the device and hit the target. Pallux does this four more times.