Doom: Eternal has a variety of different secrets available for you to locate in the game. You can collect a diverse set of toys showing off the numerous demons you’re fighting, and even obtain new soundtracks you can check out while visiting the Fortress of Doom. An important secret many players are after to complete are the slayer keys and their respective gates. Some players have noticed those are missing from their game. Slayer keys grant you access to slayer gates, where you test your skills against a fearsome challenge and massive wave of demons.
For those who finish the campaign, but were unable to complete all of the slayer keys, you can always revisit any mission you want by returning to the Fortress of Doom. On the Fortress of Doom, proceed to the front of the ship, and turn to your right. You should see a terminal there where you can access the Mission Select screen. From here, you can scroll through the missions to locate what level you missed the slayer key on, and try it again.
If you jump into a game and you notice the slayer key is missing, you want to make sure you have none of the cheat codes on. Another secret you can find in the game is several cheat codes. They enhance the game, making it easier for you to play it, such as having access to infinite ammunition or lives. All slayer gates are turned off when you use a cheat code to prevent players from using these cheats to complete these gates. You can double-check you have them all turned off by visiting the Mission Select screen on the Fortress of Doom and inspecting the screen before jumping into a mission.
Doom: Eternal also gives you the chance to play through Doom and Doom 2. Make sure to try those out when you find a spare moment by visiting the second floor of your ship, where you can find the Slayer’s private quarters.