Eternal Decks is a limited-communication cooperative game where players work together to complete stage objectives before any player is left without a legal move. Everyone starts with a small five-card deck, but players quickly acquire new cards from various Eternals—unique characters in the game who each possess their own eight-card decks.
 
On a turn, a player must perform one of three actions: play a card (onto the field, the river, or by using an ability), generate a jewel, or pass a card to a teammate. Playing cards requires careful spatial planning: across the three field rows, adjacent cards cannot share the same color or number, and individual stages introduce additional placement rules. Meanwhile, generated jewels are used to counter negative effects caused by the Eternals.
 
The game features six distinct stages, challenging players to adapt their strategies—whether collecting points, surviving a ghost town, navigating a labyrinth, or defeating a boss—to secure a team victory.