There are three types of pre-level boosters: Sticky Bomb, Bomb, and Color Bomb. In order to activate them, you should tap on their icon before the level starts.
Sticky bomb stops the entire chain for some time. In order to activate it, you need to hit it with any marble.
Bomb appears on the board along with other marbles, explodes after some time, and destroys surrounding marbles.
Color bomb removes all the marbles from the board that has identical color to the marble you used to activate it. For example, if you hit the Color Bomb with green marble, all the green marbles from the board will be removed.