Can create Mewnium Z held items for the player's Pokémon.
Held item
In battle
Allows Mew (or a Pokémon transformed into Mew) to upgrade its Psychic into the special Z-MoveGenesis Supernova. If Mew is transformed into a Pokémon other than Mew, it cannot use its exclusive Z-Move.
Unaffected by item negating effects (such as Embargo and Klutz). Item manipulating effects (such as Trick and Fling) cannot remove a Z-Crystal from a Pokémon.