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 50% of all Magic Diamonds
Completed a stage in Time Attack mode
Broke the illusion of 75 enemies
Broke the illusion of 25 enemies with projectiles
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 the Game
Completed a Castle Statue
Completed all Castle Statues
Found all the Magic Diamonds
Bounced on 7 enemies in a row without touching the ground