

Much of the enemies in The Executioner are variants of The Haunted, with the marked "bosses" being unique named characters/creatures from the main game. Unlike the rest of the game, it has a strong focus on melee combat and a plethora of thematic gear for The Keeper to utilise. Taking a departure from the third-person over-the-shoulder gameplay of The Evil Within and its previous DLCs, The Executioner is played from a first-person perspective. The last cutscene shows Marta awake in the real world, standing next to Pedro in his STEM pod, now at peace and possibly surviving the mental trauma of his self-induced separation. Pedro hesitates, but goes through with it anyway and crushes the Dark Keeper, which destroys the Keeper's own safe-head, seemingly killing him, before the screen cuts to white. Pedro battles against this "Dark Keeper", but discovers that he cannot defeat his enemy or save Marta, who the Dark Keeper is holding prisoner, unless he terminates his own avatar, at possibly the cost of his own life. In order to properly release Marta from STEM, Pedro must battle a dark manifestation of his own avatar, who plots to keep his daughter imprisoned within the dark mindscape forever. But as he goes through the first set of subjects, it becomes apparent that his daughter's own mental degradation slows, only to suddenly pick up again, even quicker than before, which MOBIUS eventually realizes is due to Pedro himself reading her notes.

Pedro's original mission is to eliminate the other rogue subjects to slow and eventually halt Marta's mental degradation, as she will be beyond saving once she hits that point. Having lost control of a new batch of test subjects, one of which is Marta Martin, they offer her father Pedro a chance to enter STEM space using the avatar of The Keeper to rescue his daughter and stabilise their system from the inside. Having collected data from the case of Leslie Withers, the MOBIUS administration wants to see if they could duplicate Ruvik's escaping methods using a new STEM system they constructed. The Executioner takes place after the conclusion of The Evil Within.
