Moloch is the only known ally of his Oni counterpart, Drahmin. Unlike Drahmin however, distorted and consumed by rage as he may be, Moloch has most likely always been a demon from the Netherrealm. The sorcerer Quan Chi confronted Moloch and Drahmin with an offer to free them from the Netherrealm if they protected him from the ninja spectre Scorpion. It was no surprise to Moloch that Drahmin accepted the offer and so they attacked Scorpion whenever he came near Quan Chi. As the two Oni were combating Scorpion, Quan Chi escaped from the dark realm without them. Enraged, Moloch and Drahmin followed Quan Chi through the portal but were transported to a different location than the sorcerer.
The Oni encountered the cyborg Cyrax in Outworld but were forced to flee from his bombs. Eventually, they took refuge in a forest and feasted on those who wandered too close to its borders. Li Mei came too close to the forest, but escaped through the trees. After that, they were enlisted by another sorcerer, Shang Tsung. They were held in the basement of his palace, as an insurance policy, should Quan Chi turn on him. Eventually, Moloch and Drahmin were set free. Instead of confronting Quan Chi, they ironically protected him by raiding Scorpion and hurling him into the Soulnado. Both Onis then disappeared from Shang Tsung's palace, as it was later destroyed by an explosion.
In his Armageddon ending, Moloch defeated Blaze and thus absorbs his power, transforming him into a Destroyer of Worlds which surpasses his own status as the Oni Destroyer but lived to the name "Destroyer." He then destroys the Pyramid of Argus and later destroys all of Edenia, turns it all into a wasteland. But because he had destroyed the portal, he was stuck in Edenia, a victim of his own destructive rage.
In Mortal Kombat's revised timeline, Moloch appears to be deceased. During one of Quan Chi's pre-fight dialogue animations in Mortal Kombat X, Quan Chi can be clearly seen holding Moloch's decapitated head.
- Beast Lord: Moloch charges at the opponent, knocking them down.
- Ground Bash: Moloch slams his orb on the ground, causing heavy damage.
- Suction Breath: Moloch creates a large gust of wind which pulls the opponent towards him, and if successful, the opponent bounces off Moloch's body and is left open for a juggle.
- Power Ball: Moloch strikes the ground with his orb and creates a projectile which strikes the opponent's legs.
- Super Charge: Moloch raises his arm into the air and roars. This heals some damage.
- Ragin' Oni: Moloch flails both his arms in the air wildly. This also heals damage.
- Furious Howl: Moloch emits a loud howl, which also heals damage.