If Kotal Kahn had a rival, I think a character inspired by a character from another culture would be ideal, as Kotal Kahn is inspired by the Aztec Indians of Mexico, so a being inspired by Anubis, the Egyptian god of the dead would be ideal, but the Mortal Kombat's Anubis would be a leader of a race of beings half human and half jackal, who should live in a kingdom based on ancient Egypt. Anubis would fight against Kotal Kahn and win him to free his kingdom from merging with Outworld, and thereby gain independence from his kingdom and his people, the jackals.