Pokémon Bank subscribers can get the Mewnium Z Z-Crystal for Mew to use its Genesis Supernova Z-Move

Pokemon Sun and Moon players who access Pokémon Bank between January 25 and October 2, 2017, will be able to claim a limited-time special Mewnium Z, the Z-Crystal for the Mythical Pokémon Mew, which cannot be obtained through normal gameplay. By giving Mewnium Z to a Mew that knows the move Psychic, it will be able to use the powerful Z-Move Genesis Supernova. This special offer is limited to one per customer, if you use Pokémon Bank with multiple copies of Pokémon Sun and Moon.