Can a climber scale a crumbling cliff before it collapses? Can a thief pick a lock before the magical alarms go off? Can a halfling rogue recover the magic goblet and escape the dragon's lair before it wakes up?
A countdown takes place when there is an unknown time limit before something occurs. A deadly ritual might need to be dispelled, or a room might be filling up with poisonous gas.
The countdown is started by forming a pool of six-sided dice. The Narrator determines the size of that dice pool based on the circumstances.
At the start of each round, the dice pool is rolled. Any dice with a result of 6 are removed from the dice pool, and play continues. The countdown is not immutable: the Narrator might deem that certain actions during the scenario might add or remove a die from the countdown, and there will often be a way to stop it. However, sometimes a countdown cannot be stopped—the cliff is going to crumble, and you must reach the top before it does!
When the last die is removed from the dice pool the countdown expires.