Nessa draws her power from the cavern's magical energy, but the caverns are slowly losing its potency. In order to replenish the cavern's magic, the priestess formed an alliance with the Dark Alchemist. This alchemist plans to siphon magic from Little Town to the caverns after his takeover. Nessa is using her powerful magics to shield and protect his forces.
Each mastery level adds another card to the cardpool for defeating Nessa. Each of the bronze, silver, and gold mastery levels unlocks a new card, while it takes all three diamond and onyx levels to unlock a single card.