A card that you will need to keep in your console’s card slot to play the game.
Many were shocked by the prices of both the Switch (€510 including Mario Kart World) and its titles (up to €90 for physical games) yesterday. This meant that another detail about the games flew a bit under the radar, although we did mention it briefly in the news story about the new cartridges, namely that physical games won’t always be so physical this Nintendo generation.
Nintendo’s Switch 2 support page clarifies that some titles will come with something called a game-key card.
