These are called Showdown Tickets and can be used to enter Showdown Tournaments. You can compete in 100-player matches clearing rounds, and the last player standing gets the Jackpot.

Each Showdown event will last only a few hours, but you can enter as many matches as you want. You get a free match entry for every event, and after that, you can use Showdown Tickets to enter.

Every Saturday, it will be accessible in the More Games tab or by clicking on the card that appears in the Home Lobby.