They are the floating crystals that appear in different spots during the game. If you play 2 minute matches they will fall at 1:02 but sometimes they don't. If you play on Plunder Island -Outside against another controller just clear out the boxes until it falls then kill eachother. There are a total of 72 Costume Balls. 24 Hat Parts,24 Head, and 24 Outfits. You start out with 4 Hats, 4 Heads, and 4 Outfits.
BE CAREFUL THE COMPUTER WILL PICK THEM UP
Credit : Zee for tips on Girl Power! and Six to Eight for tips on EXTREME MAKEOVER!