Use the following trick to unlock all the costumes pieces without having to replay a level repeatedly. Play a level that unlocks the desired costume. Just before the level ends, select "Option" and save the game on file A. Complete the level to get a random costume piece. Then, save the game on file B. Load save file A and you will be back on that level. End the level to get another random costume piece. Save the game on file B, load file A, and repeat until all costume pieces are obtained.