In Chapter 12 of Doom: The Dark Ages, players can find nine secrets and three collectibles in the Sentinel Command Station, including a codex entry, Nightmare Chainshot skin, Life sigil, Ruby, Gold chest, Life sigil, Wraithstone, Kreed Makyr toy, and more. To avoid replaying the mission to grab final items, follow this chronological guide.
In Chapter 12 of Doom: The Dark Ages, players must backtrack through areas multiple times as they navigate the complex Sentinel Command Station. This guide will help you collect all the secrets and collectibles in this chapter without having to repeat levels.
To start, head into the vent after it blows open during the mission intro, and continue straight until you drop into a rocky hallway where you can find the codex entry on the right-hand side of the room.
Next, break down the barricade in the command room to reveal a hangar area with the Nightmare Chainshot skin. After that, activate the switches in the lower levels, unlocking the first Sentinel Shrine and sending you back into the vents.
Instead of turning left, turn right to find the Life sigil hidden behind fireballs blasting at you. Move fast while keeping your shield raised to grab this collectible.
After beating the Ravager boss and collecting a demonic essence, follow the objective up the lift, but don’t go through the doors towards the yellow keycard as it triggers a point of no return. Instead, drop down the hole in the floor on the left side of the doors to find a Ruby.
Continue with the mission, grabbing the yellow keycard and jumping across the elevator into the small nook on the opposite side where you can find the Gold chest. Smash the barricade after that to reveal another sigil hidden behind it.
Next, grab the purple secret key by beating the combat challenge in the locked room, then leave the room through the main door to access a new area with the Wraithstone.
Finally, continue with the mission until you reach the hall area again, and use the hole in the stone brick wall to activate switches. With the secret key in hand, open the purple gate protecting the Kreed Makyr toy collectible.
By following this guide, players can collect all nine secrets and three collectibles in Chapter 12 without having to replay the mission multiple times.
Source: https://www.pcgamer.com/games/fps/doom-the-dark-ages-sentinel-command-station-secrets-collectibles-chapter-12