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Marosand is thought to be the result of a Sandygast forming a symbiotic bond with a Cubone that fell into its trap. This bond has allowed them both to reach their evolutions, turning them into an apex predator that throws bone shards at new victims.

Buried beneath the castle are masses of dried-up bones from those whose vitality it has drained. A Marosand is the evolved form of a Cubone that has grown tough by overcoming the grief of losing its mother.