- When you select this form of implement mastery, choose a wizard encounter attack power of your level or lower that you don’t already know. That power is now stored and available for your use at a later time. Once per encounter as a free action, you can use the stored power by expending another unused wizard encounter attack power of its level or higher. You must still take the normal action required to use the stored power. Each time you reach a level that lets you choose an encounter power, you can replace the stored power with a new wizard encounter attack power of your level or lower that you do not already know. You must wield a tome to benefit from this feature. Wizards of all builds appreciate this form of mastery because of the flexibility it allows them during combat.