Pokemon Sun and Moon brought a lot of new features to the franchise, one of the largest though was the addition of Z-Moves. These function similarly to mega evolutions, however, they power up one move for a Pokemon once per battle. They require your Pokemon to be holding a specific Z-crystal and your avatar to wear the Z-ring and to perform a dance corresponding to the Z-move being used. They also allow any Pokemon to use Z-moves as long as they hold a crystal, with a few special crystals and moves for certain Pokemon. So with the launch of the games, Nintendo also released physical Z-ring toys as well.
The Toys include three crystals to start and packs of three different crystals can be purchased to obtain the other type crystals. The big draw the toys offer is the ability to light up in response to your use of Z-moves in the game. The bracelet actually responds to the sound of your 3DS as you use an in-game Z-move and lights up based on the sound. It is a really interesting immersive feature but is a little costly at around $30 USD for the bracelet itself and roughly $5 USD for each pack of three crystals.