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 all Castle Statues
Completed the Game
Found all the Magic Diamonds
Collected all of Donald's Chili Peppers
Broke the illusion of 25 enemies with projectiles
Found 50% of all Magic Diamonds
Collected all the Magic Playing Cards
Bounced on 7 enemies in a row without touching the ground
Completed a stage in Time Attack mode
Broke the illusion of 75 enemies
Completed a Castle Statue
Collected 50 Diamonds to unlock your first Painting in the Castle