The Heroic Brutality was first introduced and is only available in Mortal Kombat vs. DC Universe. Some of the DC characters are superheroes who have sworn an oath never to take a life. As such, instead of performing Fatalities upon their defeated opponents at the end of a match when the announcer says "Finish Him/Her!", they are capable of performing Heroic Brutalities, which incapacitates and severely injures the opponent to the point that they are unable to fight any further.
The Brutality still leaves the opponent alive so that they might face justice. In general, they are not as bloody or violent as the Fatalities performed by the Mortal Kombat characters, or even the evil DC characters.