Yu-Gi-Oh Master Duel has added some new content to the Solo mode of the game. This particular one seems to be a sort of gauntlet where you play against AI decks using either a pre-made one or your own.
There are a total of 10 missions in this Gate, and you unlock each one by winning against the previous one with either deck.
Winning with a pre-made deck gives you 4 Legacy Pack Tickets for 8 of them, while one will give you the Destiny Board Mate, and the final one will grant 200 Gems. If you win with your own deck on any of them you will earn 2 Legacy Pack Tickets. Beating all the missions at least once each will give you the Magical Hats Board Parts, which modifies the Graveyard and Banished Zones.