You need to have enough DCoins. DCoins are a currency in the game which allows you to buy items, hints, levels. Here you need to unlock the "mix" level, you have to find 13 DCoins throughout the game, by playing, and purchase the mr. mix minigame. The levels will get unlocked for money. The levels that will get unlocked, are not really worth it, as in, just test maps. I show the process of unlocking the mr. mix minigame in my latest video.