The Lost Levels

Not to be confused with Lost episode (disambiguation), The Lost Mission, or the PSX Doom: The Lost Levels (add-on to the PlayStation Doom TC). The Lost Levels is a new episode for Doom 64 added in the 2020 re-release. All maps in the episode were authored by Nightdive Studios employee and Doom community member Samuel Villarreal (Kaiser).

Story
Taking place an indeterminate amount of time after the Doom marine slayed the Mother Demon in the original campaign, the beginning of the episode finds the marine stranded outside of Hell with none of his weaponry on a distant vacated UAC base. This occurred through the powers of the Mother Demon's sister, known as the Sister Resurrector, who hoped to stop his campaign against Hell by sending him away.

The marine must fight his way back into Hell, recover the Unmaker and the three Demon Keys, and then take his revenge in order to continue his quest against Hell.

The episode's ending makes reference to the Slayer Testaments of Doom (2016), implying that the journey of the Doom Slayer has begun: "A grim vision takes hold of your mind as the demon carcasses steam in your wake. Stretched before you is a path of perpetual torment... A path through DOOM..."

- Ending text

Unlocking
The Lost Levels can be accessed in a number of ways:
 * Defeating the Mother Demon on in the normal campaign.
 * Finishing and then using the "Features" menu's level select option.
 * Using any password for and then using the "Features" menu as above.
 * Using a password to access MAP34 directly.
 * On the PC version, using the command-line parameter

Levels

 * MAP34: Plant Ops
 * MAP35: Evil Sacrifice
 * MAP36: Cold Grounds
 * MAP37: Wretched Vats
 * MAP38: Thy Glory
 * MAP39: Final Judgement (Sister Resurrector is boss)

Features
One additional map is included as a "Fun" level accessible from the Features menu.
 * MAP40: Panic