Fate Core Magic Item: Srady's PennyFunction Aspect(s): There Is Always Another Trick, Size of a Mouse, Size of a Bear
Trouble Aspect: Never Changes Its Size
Srady's Penny is an ancient coin, one face is a bear and the other is a mouse. Ursyklon legend claims it had been the source of innumerable tricks employed by its creator, Srady Wiseowl. It radiates a strong transmutation aura. Until it was recovered by the Keepers, most never knew how it functioned.
Skills: Transmutation Good (+3), Nature Fair (+2), Deceit Average (+1)
"Size of a Bear!": When held with the Bear face up and the phrase "Size of a Bear" in spoken aloud in Ursyklon, Srady's Penny causes the subject to grow until they are at least ten feet tall. The subject's race aspect changes, becoming "Size of a Bear!" until the effect disappears. If the penny's other stunt is used to get rid of the effect, Size of a Mouse overrides the Size of the Bear, not cancelling it out- instead the subject shrinks to the size of a mouse.
"Size of a Mouse!": When held with the Mouse face up and the phrase "Size of a Mouse" in spoken aloud in Ursyklon, Srady's Penny causes the subject to grow until they are at least three inches tall. The subject's race aspect changes, becoming "Size of a Mouse!" until the effect disappears. If the penny's other stunt is used to get rid of the effect, "Size of a Bear!" cancels out "Size of a Mouse!", returning the subject back to their original size.
The transmutation effect is permanent. The penny's owner might be able to learn other stunts that let them use the penny in unusual or unique ways. Most importantly, Srady's Penny never can change its size. If forced to endure a transmutation effect to change it, the penny would crack and be destroyed.
In my Crux game I handle magic items like this rather liberally. If a character obtains such an item, they can use it without spending Fate Refresh. Instead, they can't invoke the item's function aspects and I have complete narrative ownership on the item unless they purchase it via a stunt. In other words, unless they pay fate refresh, nothing stops me from messing with the item. If a player buys it as a stunt, I consider them the owner and ask permission before doing anything with it.
Heavy handed, but I feel it's fair, and gets part of the magical feel of Crux across for me. This is going to be a handout for the player who owns it in question.