When you get a 100% on every level in every world, those two question mark boxes will appear with an extra bonus level and a bonus game.
Secret Bonus Levels
Get perfect scores on all 6 worlds to receive fabulous bonus games and extra levels:
World 1: Drawing Lots and "Poochy Ain't Stupid"
World 2: Scratch and Match and "Hit That Switch"
World 3: Flip Cards and "More Monkey Madness"
World 4: Match Cards and "The Impossible? Maze"
World 5: Roulette and "Kamek's Revenge"
World 6: Slot Machine and "Castles-Masterpiece Set"