You'll have to complete all 15 levels in each of the 4 worlds (60 levels total) under the Voodoo time (for the Time Attack stages, the remaining time on the timer when you complete the level must be over the Voodoo time). Once you've grasped the concept of how to maneuver your dice in order for it to show the right number on the square you want, completing levels under the voodoo time becomes considerably easier. When all else fails, just keep moving the dice in different square/rectangle patterns to lock in the number you need. It's also recommended on the seemingly more complex levels to map out the entire area to see if there is an easier way to complete the level. Some maps contain more items then what you really need to use on order to complete a stage quickly.
A Voodoo Time video guide for all levels can be found HERE.