If held by a Scizor, allows it to Mega Evolve into Mega Scizor if its Trainer has a Key Stone. Each Trainer can only Mega Evolve one Pokémon per battle.
Unaffected by item negating effects (such as Embargo and Klutz). Item manipulating effects (such as Trick and Fling) cannot give Scizor a Scizorite or remove a Scizorite from Scizor.
Outside of battle
If held by a Scizor, allows it to Mega Evolve into Mega Scizor when it performs a Spectacular Talent during a Pokémon Contest Spectacular while its Trainer has a Key Stone. Scizor will remain a Mega Scizor until the Talent Round ends.