Limited charges. After any scene in which this item is used, roll a single d4 (unmodified). On a roll of 1, the item ceases to function until it can be recharged.

(Better recharging methods could allow a higher die for this check.)

Limited use. After any scene in which this item is actively used to create a guise, roll a single d6 (unmodified). On a roll of 1, the magic of the stone has faded.