A doubling-cube feature.
Before your turn, you can offer to double the stakes.
- If the opponent accepts, the game continues and is now worth twice as much for the purposes of rank calculations;
- If the opponent refuses, the game immediately ends as if they had resigned.
A player cannot double twice in a row: when A plays against B, if the game has already been doubled at least once and A was the last player to offer to double, then only B can offer to double.