As Carl’s father’s trailer burns, Carl and Donut prepare for the keyholder fight. Carl notices other crawlers are still trapped in personal memories, meaning Carl and Donut will be the first to learn what happens when the timer ends. Donut casts Clockwork Triplicate on Mongo while Carl lays traps, but Carl remains distracted by the memory of Asher, his newly discovered half-brother, and fears the dungeon might use Asher as the boss.

The trailer collapses and reveals the key master: the Reminiscence Hydra of Malicious Compliance, a level 125 city boss made of nine familiar heads, including Asher, Tami-Lynn, Bea’s mother, Carl’s former boss Dick, his landlord Mr. Roth, coworker Sally, Monobrow Sam, Donut’s relative Sugar Cube, and Judge Lucian. The AI interrupts with a long explanation, revealing that the intended boss was Carl’s father but that the AI chose this monster instead, exploiting rules against using reconstituted loved ones by altering one molecule. The AI also exposes information about mantises, macro AIs, and attempts to create more stable AI systems.

Judge Lucian acts as the hydra’s deckmaster, breaking invisibility and summoning totems. Donut answers with her own card summons, including Jola, Geraldo, and later Shi Maria, while Carl tries to identify which head provides fire resistance. The hydra heads attack with distinct powers: Asher uses lightning, Sally sprays acid, Monobrow Sam fires a death ray, Dick uses water, and Judge Lucian uses anti-magic/card effects. Alpha Male Carl and King Croissant appear as enemy totems, mocking Carl and Donut while destroying Donut’s clockwork Mongo copies and damaging Jola.

Following Mordecai’s advice, Carl realizes the hydra’s body cannot be harmed until the fire-resistant head is removed and the wound cauterized. Carl identifies Bea’s mother as the likely fire head, moves in with a snap collar and Chaco’s shrink wand, and decapitates her just as she prepares a fire attack. Carl then smashes flaming moonshine onto the wound, causing the hydra’s own flames to finally damage it, but Carl is badly burned and loses invisibility.

Shi Maria tears off several heads, including Sugar Cube, Mr. Roth, and Asher. Before killing Asher’s head, Shi Maria reads Carl’s thoughts through her opened third eye and tells Carl that Asher’s echo rests, while warning that Carl will soon do something for Shi Maria. Monobrow Sam’s death rays and the stolen clockwork staff destroy Shi Maria’s totem form, but she returns to Donut’s deck through a Cockroach ability. Raul briefly appears and tries to extinguish Carl’s flames before Alpha Male Carl kills him, then Mongo knocks Alpha Carl away as the enemy totem times out.

With only Judge Lucian and Tami-Lynn left, the hydra collapses under the spreading fire. Tami-Lynn tells Carl she does not regret killing his father, claiming she did it so Asher would not suffer as Carl had. Judge Lucian dies, the hydra bursts apart in gore, and Carl and Donut win the combat.