: Accessing the Doom Slayer's in-game computer allows you to unlock full versions of original games; for example, entering the code FLYNNTAGGART unlocks DOOM II .
In , the Codex serves as a mobile database that provides lore and technical details on the game's world.
: Collecting certain Codex entries or completing related challenges can reward players with Sentinel Crystals to upgrade health, armor, or ammo capacity.