The Portal in front of the 3 skull-headed statue of Kochal that opens after defeating Kobra, Kira and Kabal
Kochal is a three-headed demon god, as described by an Oni in the Netherrealm. He was said to be an actual being within the Mortal Kombat universe, and was a rumored super unlockable in Mortal Kombat: Deception soon after its release. It was soon discovered that is was nothing but a Koin rewarded challenge.
About
Shujinko while in the Netherrealm, found an altar to Kochal, the 3-faced demon god of the Chaosrealm
Rumors of Kochal's existence began circulating due to three missions (challenges) in the Netherrealm, which involved defeating members of the Black Dragon clan (Kobra, Kira, and Kabal) to "awaken Kochal." Furthermore, some of the Oni in the Netherrealm would at times speak of Kochal after interacting. They claimed that Kochal was a three-headed god who would transport Oni to a sorcerer who needed them. As for the challenges, behind the platforms that Kobra, Kira, and Kabal stand upon, are three giant skulls, which begins to pour lava from their mouths after each member is defeated. When Kochal "awakens," or more accurately, when the challenge is complete, the portal opens and transports the user back to the sorcerer village near the portal used to enter the Netherrealm. The challenger would be greeted by a chest of 1000 Onyx Koins.
Koin Challenge
Kochal is often theorized by some fans to mean "KOin CHALlenge", because of the reward of koins earned after defeating the Black Dragon trio, though this has never explicitly been stated by the Mortal Kombat production staff. While Kochal is presumably not a real character, there is also absolutely no hard proof that the word stands for "Koin Challenge," or that Kochal is not a real character. However, while only contemporarily theorized, the fact 'Kochal' means 'koin challenge' is still a distinct possibility, since this is a naming method commonly used by the Mortal Kombat creators for characters, such as, for example, Ex: ERror MACro refers to Ermac, and MOtion KAPture refers to Mokap, who is based upon (or actually is) Carlos Pesina, a motion capture worker. It should also be noted that Kochal's name, like the known Black Dragon members (Kano, Kabal, Kira, and Kobra) starts with the letter K.