Super Gore Nest

The Super Gore Nest is the fifth level of Doom Eternal. The Doom Slayer travels to an infested cityscape in central Europe where the demons have constructed a gigantic gore nest from the remains of their innumerable victims, which must be destroyed to slow Earth's consumption by Hell. The buff totem and spectre enemies are introduced in this level, along with the chaingun weapon.

"With the elimination of Deag Ranak, only one Hell Priest remains. As you prepare for the final encounter with the remaining Priest, your plans are interrupted by the Khan Maykr. In an attempt to ensure the consumption of Earth, she has hidden the Priest and accelerated Hell's invasion of the planet. The increased number of demons overflowing from the Super Gore Nest threatens to overtake Earth - gain access to the nest and destroy it before it's too late."

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Lore
The Super Gore Nest was created through a ritual conducted by UAC cultists under the command of Deag Ranak, which dramatically accelerated the development of a Hellgrowth within the reactor chamber of a UAC facility in central Europe. Its location is the initial origin point of the invasion of Earth, and the Hell portal sustained by the gore nest is capable of allowing millions of demons to pass through the void.

In an attempt to destroy the nest, four US Battle Mech divisions, the Con-EUR Long Range Naval Artillery Barrage Fleet, 27 US Night Bird Apaches, three NATO Shock Troop battalions, two CON-EUR Rapid Response Levi-Tank divisions, and 18,000 coalition Special Forces units sacrificed themselves; however, they failed in their effort.

Tyrant battle Easter egg
After clearing the final arena and using the last two gore keys, reload the checkpoint. Within the arena are three birthday party balloons, all of which must be shot: Popping all three balloons will cause a booing crowd sound effect to play and an unusual red-colored "secret found" notification will appear. The central area of the arena just beneath the gore key podiums will now contain a birthday cake (the same blue-and-green-frosted cake previously found in the Titan's Realm in Doom (2016)) and an apparent soulsphere.
 * One is located high to the right edge of the arena behind the arm of a crippled mech;
 * The second balloon is beneath a wrecked bus partially submerged into the lava adjacent to the soulsphere island near the center of the arena;
 * The final balloon is located far to the lower left of the arena, beneath the blue gore key bridge inside a pipe.

Trying to take the soulsphere on top of the cake will cause it and the cake to vanish, and two tyrants will warp in. This secret battle contains no fodder demons, making it more difficult than this would otherwise imply. Nothing is gained by defeating the tyrants.

Pre-release
Super Gore Nest was the first 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 Doom Slayer puts on his helmet and inspects both his Doomblade and super shotgun as the play-through begins. The final game inspects the super shotgun at an earlier level, Cultist Base as part of a required objective. The helmet is put on and the Doomblade is inspected as part of the opening cinematic of the game on the Fortress of Doom.
 * Shortly after the first encounter during the level, the Doom Slayer picks up the combat shotgun and inspects it. The final version of the level excludes the weapon itself (as it is the starting weapon), and the inspection animation is never seen (unless if cheats or console commands are used). Notably, the pickup model of the shotgun is akin to Doom (2016) as opposed to the stylized pickups found in the final game.
 * Likewise, the rocket launcher is introduced later on in the level, as opposed to the Cultist Base. Like the shotgun, the rocket launcher is seen on the ground instead floating.
 * The arachnotron is introduced in a cutscene, akin to monster introductions in Doom (2016). This is not the case for the final version, where the arachnotron was introduced in the first level, Hell on Earth. A dread knight is found in this location in the final level.
 * The second segment introduces the blood punch as a pickup, using a floating orb somewhat similar to the final game's rune stations. In the final game, the blood punch is acquired from a special pickup on Exultia.

Master Level
A Master Level version of this mission was released with Update 4 on, which makes a number of changes designed to significantly increase the level's difficulty:
 * The number of enemies is significantly increased, with much greater use of tentacles and carcasses. The Master Level also adds enemies which are normally found later in the game, including tyrants, marauders, arch-viles and barons of Hell.
 * Elements from The Ancient Gods, Part One, including whiplash spectres and heavy fog, are used at certain points in the level.
 * The room under the chamber that held the chaingun is now filled with toxic water, along with part of the escape route used at the end of the level.
 * Ten challenges are introduced which require the player to complete the level at different difficulties, including Ultra-Nightmare. A "Classic Mode" is also introduced, where the player starts with an unmodified combat shotgun and must collect more weapons and modifications as they progress. Completing all ten challenges unlocks a golden skin for the combat shotgun. Each individual challenge also has its own cosmetic item unlock.

Trivia

 * Two of the Fast Travel destinations in this level are named "Toxin Refinery" and "Industrial Zone". They may refer to the Doom and Doom II levels of the same names, but may be coincidential.