Stage Brutalities are a new type of finisher introduced in Mortal Kombat X. While not originally in the launch version of the game, they were included in the May 15th update as hidden finishers.
Bearing some similiarities to Stage Fatalities, Stage Brutalities allows the player to use an interactable object from the played stage to abruptly kill the opponent, causing an immediate victory.
Stage Brutalities follow the same mechanic used for Brutalities in Mortal Kombat X, requiring certain conditions and set ups to be met. Typically, at least two other Stage Interactions have to be used before the final, with the specific interaction being thrown at the opponent when their health is low enough to trigger the Stage Brutality.