Effect
A mysterious box made by Silph Co.
Level up Porygon while holding this to get Porygon2. Better bulk than Porygon, and can run Eviolite still for even more defenses!
There's one at Silph Co. in Saffron City. If you want Porygon-Z later that needs a Dubious Disc instead - different evolution.
Game:Polished Crystal
