GWENT: The Witcher Card Game

In order to do this, you have to buy your way into the Arena. It costs Ore, which you can get from spending reward points and playing multiplayer matches. Once you are in, the Arena requires that you either lose 3 times, or win every match, whichever comes first. Either outcome will give you the achievement.

If you are going for this achievement actively, you can just pass each round to lose three matches in a row. I am not sure if pausing and backing out counts, but that may be possible too. You can obviously play naturally or try to win as well, passing and loosing is just the fastest solution.

Once you have met either requirement, the contract is completed and the achievement is yours.

EDIT: I'm not sure why this is being downvoted. This is the fastest way to unlock the achievement. This isn't the place for an in-depth discussion on how to win matches and the meta of the game.