Here is the full list of all 12 Castle of Illusion achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Completed a stage in Time Attack mode
Completed the Game
Found 50% of all Magic Diamonds
Broke the illusion of 25 enemies with projectiles
Broke the illusion of 75 enemies
Collected 50 Diamonds to unlock your first Painting in the Castle
Collected all the Magic Playing Cards
Collected all of Donald's Chili Peppers
Completed a Castle Statue
Completed all Castle Statues
Found all the Magic Diamonds
Bounced on 7 enemies in a row without touching the ground