To expand the den, it costs apples, which can be purchased with real money, from other pack's market dens with about 1500 mushrooms per apple, and from trades. Along with selling wolves for apples and winning certain contests that are open with an apple prize. If you get the apples needed, the place to expand is in Barter> Apples. The cost is 20 apples, which adds 5 den slots.

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