Mars Core

Mars Core is the seventh level of Doom Eternal. Beginning at the orbital defense base on the moon of Phobos, the Doom Slayer battles an ongoing invasion while intending to reach the core of Mars, where an ancient Night Sentinel slipgate resides. Through the use of an orbital weapon system known as the BFG-10000, the planet Mars itself suffers massive damage, directly creating a path to its core.

Pre-release
A shortened version of the first half of Mars Core was the second level of Doom Eternal to be displayed to the public in the BE3 reveal on.

The noticeable differences from the reveal to the final product includes the following:
 * The player takes control of the Doom Slayer before walking inside the elevator, as opposed to starting inside the elevator in the final version.
 * The PA system inside the Phobos outpost has a different voice actor.
 * The exclusion of the green cracks before exiting out of a vent during the reveal.
 * The exclusion of the UAC Spokesperson hologram before exiting outside.
 * The exclusion of a 1-Up outside.
 * The exclusion of Samuel Hayden and VEGA throughout the level, presumably to avoid spoilers.
 * The exclusion of the Doom hunter and dread knights near the BFG-10000.
 * The exclusion of the chaingun throughout the level, likely being developed at that time. The final version introduces the chaingun as a mandatory pickup in Super Gore Nest to advance the level, although the part of the level itself was not seen at that time, further supporting the theory.
 * The main entrance to the BFG-10000 is accessible in the reveal, which contains an arch-vile. The Doom Slayer pulls out and swings his Crucible blade in a cinematic, after which the reveal ended. In the final version, however, the main entrance is inaccessible and a maintenance hatch underneath is taken instead. Both the arch-vile and the crucible blade are introduced later, on Taras Nabad.