The Doom Slayer returns to Hell in order to gain access to the Dark Lord's life sphere, against the advice of the Intern. Fighting his way through the Blood Swamps, the Slayer completes the Trials of Maligog by interacting with two ghostly Night Sentinels at different ends of the swamp. He is then teleported back to the centre of the swamp where he completes the last Trial of Maligog in combat.
After beating the trials, an enormous Titan lifts the platform the Doom Slayer is standing on and transports him to the sanctum which holds both the Father and Dark Lord's life spheres. Here, the Slayer meets Samur Maykr who pleads with him to restore the Father. Ignoring the Seraphim's wishes, the Slayer destroys the Father's life sphere - preventing his return - and instead takes the Dark Lord's life sphere back to the ARC Carrier.
Completing both secret encounters on this level unlocks the Wetland Warrior skin for the Doom Slayer. Additionally, completing the level on Nightmare unlocks a new main menu background. The Betruger Castle area of the level is likely a reference to Malcolm Betruger from Doom 3. Likewise, the Ishii Keep area of the level is presumably a reference to the character Jonathan Ishii.
Despite what one might expect, the Betruger Castle quest is significantly easier than Ishii Keep, with about half as many monsters.
