The Randomizer booster unlocks at Level 36. This powerful booster redeals every remaining card on the board, keeping all your cards in their current positions but changing their letters. It's great for when you find yourself with a yucky board with lots of hard-to-use letters like V's and K's.

Note that the Randomizer booster does not affect the Draw Pile, and that you can only use the Randomizer booster when your letter tray is empty.