I hope this hasnt been made, buuuuut...
Mine would be:
Trinity Synchro
Sora, Donald, and Goofy all jump into the air, and they would fly for a few seconds, circling around the area. Cloud would be summoned, and then they would all land. They would all then perform Sonic Blade in a perfect star formation all over the stage, leaving a white symbol on the ground. Cloud would dissapear again. Once stepped in, the symbol would heal the party, and would place small angel feathers on the party's shoes, making them all faster for a short while until the symbol dissapeared.
Magic usage: 3 units from Sora, 3 from Donald, and 1 from Goofy.
Extra: Ultima Keyblade, Save the Queen, and Save the King all need to be equipped on the proper party member.