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Within the Phendrana Drifts lies the quarantine cave. In the cave lies an enormous pile of boulders. When you go up to this pile, it will react and come alive to become the boulder monster, Thardus. Thardus can throw minor boulders, freeze you in the ground, control the weather, and roll like a boulder, attempting to hit you. Once you have defeated Thardus, he will give up the Spider Ball ability to you.