Cobalion's nature depletes Attack, so a Calm Mind set alongside Flash Cannon / Focus Blast / Substitute is the best it can do. However, you can still run a purely Physical set to take advantage of it's superior Physical Movepool with Swords Dance / Close Combat / Stone Edge / Iron Head. It is more of a personal preference.
Latias' Attack is below average, and Bold further lowers it, so stick to Special Moves. Dragon Pulse > Waterfall and Calm Mind > Psychic or Fly, depends on which one you need more.
RK9 has Jolly, so you should mainly stick to Physical Moves. Crunch / Flare Blitz / ExtremeSpeed / Wild Charge will do.
I'm feelin' electric tonight
Cruising down the coast goin' 'bout 99
Got my bad baby by my heavenly side
I know if I go, I'll die happy tonight