Dark Kahn

Dark Kahn is the primary antagonist in Mortal Kombat Vs. DC Universe. He is the combined form of both, Shao Kahn, and Darkseid.

Darkseid
Darkseid and his Parademons were defeated by Superman. Darkseid tried to escape by using a portal, but Superman used his heat vision and disrupted the portal, causing it to explode, with Darkseid in it. Superman thought that Darkseid was killed. However, Darkseid didn't die; instead he merged with Shao Kahn and they became Dark Kahn.

Shao Kahn
After Shao Kahn was humiliated by his defeat at the hands of Raiden, he attempted to escape. But Raiden shot Shao Kahn with a bolt of lightning causing the portal to explode, with Shao Kahn inside it. Raiden thought that Shao Kahn was dead. However, Shao Kahn didn't die: instead he merged with Darkseid and they became Dark Kahn.

The Confrontation
Dark Kahn didn't appear until the very end of both story modes. When the Mortal Kombat Kharacters, and the DC Universe Characters entered the merged world of Apokolips and Outworld, Dark Kahn expected them. He used his power of rage and force everyone to fight each other. All were standing were Superman, and Raiden. When they two were about to fight Dark Khan, he use his rage so they can fight each other. They manage to fight over the rage and they decided to team up and fight Dark Khan. When Dark Kahn was defeated everything was back to normal, except of two differences; Darkseid was in the Mortal Kombat World, while Shao Kahn in the DC Universe World. When they were in the other worlds, they have no powers so they were easily imprisoned by the main heroes.