Mystery bonuses can be triggered by randomly selected times, amounts of play or jackpot size. On games with skill-based bonuses, skilled players will do better than unskilled players, but do not have an edge on the house.
Well, slots with the bonus buy function implemented in the game offer the players to buy and directly enter the main Bonus. If you are one of those players who doesn't like to wait for the scatters and bonus symbols to align on the reels, then this option is perfect for you.