Refers to a scenario change that surprises everyone involved.

Unexpected Turn

Represents a factor that dramatically alters the current situation or strategy.

Game Changer

Suggests a risky component that could lead to unpredictable outcomes.

Indicates a surprise element that could provide an unforeseen advantage.

Something or someone underestimated but holds significant potential to effect change.

Though unpredictable, the phrase does not necessarily imply a negative impact.