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, and the Phobos base is evidently destroyed, being mixed in orbit with portions of facilities blasted from the surface.

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:
 * Exclusion of Samuel Hayden throughout the level, presumbably to avoid spoilers.
 * The entrance to the BFG-10000 is accessible in the reveal, which reveals an arch-vile at the other side of the door with the Doom Slayer pulling out and swinging his Crucible blade as the reveal ended in a cinematic fashion. In the final version however, the entrance is inaccessible, as the Doom Slayer takes the maintenance hatch is taken instead. Both the arch-vile and the Crucible blade are also introduced later.