Doom: Eternal has a variety of different secrets at your disposal in the game. You can collect a diverse set of toys showing the many demons you fight, and even get new soundtracks which you can discover by visiting the Fortress of Doom. An important secret that many gamers look for are the Killer Keys and their respective doors. Some players have noticed that they are missing from their game. Slayer Keys give you access to Slayer Gates, where you test your skills against a spooky challenge and a massive wave of demons.
For those who have completed the campaign, but weren't able to complete all of the Killer Keys, you can always revisit any mission you want by returning to the Fortress of Doom. On Doom Fortress, go to the front of the ship and turn right. You should see a terminal where you can access the Mission Select screen. From there you can scroll through the missions to locate the level you missed the Slayer key and try again.
If you jump into a game and notice that the Slayer key is missing, you want to make sure that you don't have any of the cheat codes. Another secret that you can find in the game is several cheat codes. They enhance the game, making it easier for you to read, like accessing ammo or endless lives. To prevent players from using these cheats to complete these doors, all killer doors are disabled when using a cheat code. You can verify you've turned them all off by visiting the Fortress of Doom Mission Select screen and inspecting the screen before embarking on a mission.
Doom: Eternal also gives you the option to play through Doom and Doom 2. Be sure to try them out when you find some free time by visiting the second floor of your ship, where you can find the Slayer's private quarters.
