There are two entrances to the next room of interest.
More commonly this will be executed through the previously 'broken' door after which lies a short corridor to the pod room where the "Oso thing" makes a final appearance, (having followed the player through Lab X-2 with various tidbits of braggadocio and junk-info)
A few stray Zombies may need dealing with and this would be preferable before entering the pod room, as they may interfere with the player during the first cutscene.
Walking into the pod room triggers the appearance of the "Oso thing" who initially launches into a diatribe concerning existence. Part of the diatribe is poorly mixed with the sound dimmed by at least 20dB.
The "Oso thing" - until this point manifesting its human form familiar to that seen in the release game, now transforms into a Pyrogeist in order to harass the player.
Shooting the human manifestation would be counter-productive.
After a brief attack with fire traps the beast retreats to one end of the chamber and just lurks there.
Although the Pyrogeist is susceptible to bullets, any grenade that the player may have in reserve will be highly effective.
Death of the Pyro form of the 'Oso-thing" triggers a cutscene where the holographic humaniform 'dies' leaving the player to conclude the mission up the staircase.
Crossing the threshold into the upstairs generators control room triggers a cutscene where the player's actor approaches the PC, ostensibly enters the code from the Generators doc and releases control back to the player to conclude the mission.
Whether the player "throws the switch" or just dodges around the Teleport is optional. Once through the Teleport there is no returning. This will be the point where the player decides to get to some form of ending. Or not.