Question: what are the z crystals?
Answer: A Z-Crystal (Japanese: Ｚクリスタル Z-Crystal) is an item required to upgrade moves to Z-Moves through the use of a Z-RingSM or Z-Power RingUSUM. In the Alola region, Z-Crystals play an important role in the island challenge, as they provide proof of completing trials and grand trials, much like Gym Badges in other regions.