The battles you can get Mickey in are:
Shan Yu- Land of Dragons
Storm Rider- Land of Dragons
Dark Stalker- Beast's Castle
Black Thorn- Beast's Castle
Xaldin- Beast's Castle
Cerberus- Olympus Coliseum
Hydra- Olympus Coliseum
Volcano Lord and Blizzard Lord- Agrabah
Grim Reaper- Port Royal
Xemnas in Armor- The World That Never Was