The Nightmare Express's dangerously deteriorated steam boiler, primed to explode when dead engineers leave its pressure unchecked.
After the Protective Shell ambush kills both engineers, the Nightmare Express accelerates with five pressure gauges nearing red. Lowering the throttle worsens the pressure, and the control station identifies the boiler as a deteriorating Shattering Train Bomb with roughly two minutes remaining.
Fire Brandy directs Carl through the correct valve sequence, returning the gauges to green and removing the explosion warning before teaching him safe operation.
A massive black locomotive boiler surrounded by brass valves, levers, pipes, and five pressure gauges climbing toward the red.
The boiler turns Carl's successful monster attack into an immediate second survival puzzle.