>>36921849That's half of it.
Z-Moves are performed by holding a certain item, which acts sort of like a mega stone does (can't be removed from the Pokemon during a fight, and limited to one per team.)
Z-crystals turn moves that share their type into Z-Moves. For damaging moves, this just turns the move into a generic nuke with an insane bp that depends on the move's base bp. For status moves, it'll cause additional effects depending on the move (Some notable ones include Z-Splash increasing your attack by 3 stages and Z-Celebrate and Z-Conversion acting as a free Ancient Power boost.)
