Kombat Rage was a kombat element and an integral part of the story of Mortal Kombat vs. DC Universe.
In The Story
The Kombat Rage is the main part of the Story Mode. It came to both universes after the creation of Dark Kahn. Once influenced by the rage, the warrior consumed by it sees his/her worst enemy (as seen through Liu Kang's perspective in the DC Universe story). Because of the hallucinations, a kombatant could fight his best friend. Throughout the story, the Rage would switch fighters after the current host would be defeated in combat. Up until the last scene, each side attempts to uncover the source, thinking it lies with the other universe after the merging of the two. At the last scenes, both universes kombat each other as a group. Only Raiden and Superman survived, with each about to kill their main enemies, but being stopped by their best ally, both of which would later fight and defeat as a result. Upon the victory, the two venture to Dark Kahn's fortress, and fight each other to see who would kombat Dark Kahn (although the actual contender is from the perspective the player chooses). After destroying Dark Kahn, the two universes end the merging.
In Arcade mode, the rage can significantly be good or bad for the fighter. During combat, Rage can be built up by the kombatant. Located under the health, there is a small yellow bar that can be filled up. To fill it up, the player must be attacked a lot, have the opponent block their attacks, and have the opponent use special moves on them (or a move that fill up the meter such as Joker's Funnyman and Dark Kahn's Enrage). Once the meter is filled up, it will start to glow with energy. When activated, the player's attacks are doubled in damage, while the player still loses normal amount of health. In addition to the fighter's new found strength, their body will also glow with the energy. Also, the player is more stable, meaning he/she isn't more prone to launching, and falling. Also, the player that delivers the first hit will have their meter filled up halfway.
In Injustice: Gods Among Us
Shazam's (Captain Marvel) ending in the arcade mode shows the hero's friends becoming violent and turning against their fellow crime fighters, due to an "alien virus" that give them mental instability. In addition, those who are infected by that virus have their eyes glowing yellow, like what exactly the Kombat Rage do. Shazam shared the power of the Word to his adopted siblings and together, they manage to defeat the heroes, even replacing them as the new league of heroes. It is unknown if those who were infected by the virus are still alive, however it is stated Shazam and his army manage to incapacitated them.