At the beginning of a game, put down the d12 or d20 and set it to 11. This is the doomsday clock. At the end of every round, the doomsday clock counts down by one.
In order from highest current score to lowest, each player chooses to count down the DDC by 1 or to pass. When the DDC reaches 0, the battle ends, and the player with the highest score wins.
While ties are possible, but unlikely, resolve them by either going one more turn or counting who has the most assets left.
Whoever has the highest score will want to advance the DDC, whoever has a lower score will not.