There's one move that varied per boss battle...
G4 called it "The Gimmick move" and said that it was a specific action you could only do at certain time during boss battles. Such as when you fight the dragon in Mulan world, when he dives, you use the gimmick move to use the air currents and jump onto the dragons back and attack his horns, which is his weakness. When fighting Cerberus, you can use this command to jump between two of the heads, and continually slash at the middle head, then jump into the air and do a mid-air combo.
Then there's the triangle command. This is the command used to activate ability's. In the last game, if you wanted to use a move like "Ragnorok", you would have to wait till the word "Ragnorok" appeared in the 4th box on the command menu, select it, and target the heartless you wanted to use it against. Now all you have to do is press triangle when the symbol appears over your targets head, and bam, your using your ability...
I nkow of one move you can do when fused with Donald calld "Comet Rain". From the sound of the name and a screenshot I saw, it looks like it sends a rain of comets (Go figure, eh?) that destroys everything in front og you.
And when fused with goofy (Brave/Valor Form) theres suppose to be a series of techniques called Grenade, Grenara, and Grenega.