Well, i'm pretty sure you got the boss fights he appears in but i've got some other info. The odds of King Mickey appearing to help you decrease with every use of the little critter. The first time you die on one of the specified boss battles, he has a 100% change of appearing. If you continue but die again (even later in the game) on one of the specified fights, you have an 80% chance of him coming to help. The third time you have a 64% chance of getting him and the fourth time onward you have a 50% chance of getting him. The percentages don't reset unless you load a previously saved game. So, if you die, use Mickey, and than beat the boss and save the game, your odds have gone down for next time.