Unlimited Boosters can be earned as a reward in the game. Once obtained, a specific type of pre-level booster will be limitless for this buff on Saga map levels.

You can check remaining time until it expires by selecting a level on the Saga map, and taking a look at the pre-level boosters where one of them should have a timer visible. As long as this timer is active, you can use such pre-level booster without any limits, and it will be automatically activated on levels available on the Saga map.

IMPORTANT: For example, if 30 minutes of Unlimited Bomb Pre-Level boosters buff is active, then none of the coins or pre-level boosters of this type are going to be used from your inventory.