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.
Found all the Magic Diamonds
Completed all Castle Statues
Collected all the Magic Playing Cards
Bounced on 7 enemies in a row without touching the ground
Completed a stage in Time Attack mode
Completed the Game
Collected all of Donald's Chili Peppers
Found 50% of all Magic Diamonds
Completed a Castle Statue
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