Gwent Master is an achievement in The Witcher 3: Wild Hunt and requires one to defeat Tybalt and win the gwent tournament held at the Passiflora. In this case, it means you must complete the secondary quest High Stakes and win, thus making this a missable achievement.

Tips

• You won't be able to replay if you lose, so be sure to save between matches after you win each one.
• It's highly recommended to make sure you have a strong deck.
• Many of your opponents make good use of spy cards, so make sure you can counter them for your own benefit.
• Heed the rules: once you start the tournament, do not leave Passiflora or else it'll fail, locking you out of the achievement.
• This achievement goes well with Card Collector.