Despite having defeated the Icon of Sin and halting Hell’s invasion of Earth, the Doom Slayer’s victory over the Demons did not come without cost. The death of the Khan Makyr and Hell’s conquest of Urdak have given the demons a chance to dominate all dimensions and reinitiate their invasion of Earth. To prevent this, the Doom Slayer, along with Samuel Hayden and ARC scientists, embark on a mission to find and liberate the Slayer’s ally, the Seraphim. Traveling by sea on an ARC Carrier towards the UAC Atlantica Facility, the Slayer fights his way to the Seraphim's containment pod. When Hayden requests he be uploaded into the pod, it is revealed that he and the Seraphim are one and the same.
After returning to the ARC Carrier, the Seraphim tasks the Slayer to find and retrieve the Father’s Life Sphere from the Blood Swamps of Hell in order to return the Father to physical form. After fighting his way through the Blood Swamps, the Slayer finds and retrieves the Father’s Life Sphere. However, the Slayer chooses to destroy the sphere rather than hand it to the Seraphim and instead retrieves the Dark Lord’s Life Sphere before returning to the ARC Carrier.
Despite most of the Carrier’s crew evacuating upon seeing the Dark Lord’s Life Sphere, a lone intern stays to help the Slayer reach Urdak assuming that the Slayer intends to resurrect and destroy the Dark Lord, which in effect will destroy all Demons. Upon reaching the corrupted Urdak, the Doom Slayer fights his way to the Luminarium where anyone who has a Life Sphere may activate it. However, the Slayer is confronted by the Seraphim upon reaching the Luminarium’s entrance. Consumed by Urdak’s demonic corruption, the Seraphim is transformed into a Demon and after a lengthy battle is ultimately defeated by the Slayer and is teleported away by the Father. Despite being warned that bringing the Dark Lord into physical form is irreversible, the Doom Slayer proceeds to summon him, the creature manifesting as a copy of the Slayer himself.
The Ancient Gods DLC features all the Non-Boss enemies previously from Doom Eternal while also including some new additions.
The Ancient Gods DLC features all the weapons that were obtained from the base campaign, with the exception of the Crucible, as the blade was broken off by the Slayer to kill the Icon of Sin in the climax of Doom Eternal.
ARC Carrier (Cutscenes/Intermission)
- Doom Eternal "Ancient Gods" DLC Announced, GameSpot, Retrieved August 11, 2020