Every time you begin a new challenge, you'll be presented with an opportunity to wager shells. Here's how it works: when you open your challenge, you choose the difficulty of the challenge (easy, medium, hard), then you choose your wager amount (100 shells, 500 shells, 1,000 shells, or 2,500 shells).
We like to tell players that wagering is a lot like gambling: a wager is not a guarantee that you will win shells or that you will even win your initial shell wager back, but you can make wagering work in your favor by purchasing eggs as you complete the challenge or else increasing the difficulty of your challenge. Keep in mind—the greater the risk, the greater the payout!
Want to know more about challenges? Read more about them here.