The animated superhero series Invincible continues its fourth season on Prime Video, and Episode 4 takes viewers on a surprising trip to the Underrealm. Titled “Hurm,” the episode brings back a familiar face from Season 1—Damien Darkblood—while introducing new characters and expanding the show’s mythology beyond what was seen in the original comics. The episode arrived on March 25, 2026, and follows Mark Grayson as he gets pulled into a demonic civil war that threatens both Hell and Earth.
What Happens When Damien Darkblood Returns
Damien Darkblood, the demon detective first introduced in Season 1 investigating the Guardians of the Globe murders, makes his return in Episode 4. But this time, he is not on Earth solving crimes. Instead, he is in the Underrealm, leading his clan in a battle against a powerful warrior named Volcanikka.
The episode explains that Darkblood was sent back to Hell by Cecil Stedman after he got too close to discovering the truth about Omni-Man in Season 1. Now, he finds himself in the middle of a civil war. Volcanikka has taken control of the Underrealm from Satan himself and is searching for an object called the Vial, which would allow her to release ancient monsters called the Vile onto Earth’s surface.
Desperate for help, Darkblood convinces Satan to summon a powerful warrior from Earth. The ritual uses blood from the Guardians’ crime scene, aiming to bring Omni-Man. Instead, it pulls Mark Grayson away from a fight on Earth and into the depths of Hell.
The Underrealm Is Different From What You Might Expect
The version of Hell shown in Invincible Season 4 Episode 4 is not the fiery pit of punishment from religious texts. The Underrealm is described as a massive pocket dimension located deep within the Earth’s core, so far down that flying out would crush anyone before they reached the surface.
The ruler of this realm is Satan, voiced by horror icon Bruce Campbell. But Satan is not portrayed as an evil figure. Instead, he is shown as a ruler trying to maintain order among a million demons. The episode reveals a complex cosmology where humans are the sixth age of existence. Demons like Darkblood come from the fifth age, and before them were the Vile—monstrous creatures the demons fought for thousands of years before trapping them in the deepest part of the underworld.
One of the more surprising moments comes when Darkblood tells Mark that there is no Heaven in this universe. He advises Mark to focus on making his own world better rather than waiting for an afterlife.
Mark Grayson Learns a Lesson About Being a Hero
The trip to Hell gives Mark time to reflect on his recent actions. He has been struggling with guilt after killing an astronaut in a previous episode and worrying that he is becoming like his father, Omni-Man.
During his journey with Darkblood, Mark opens up about his fears. Darkblood tells him he is different from Omni-Man because he actually asks questions and thinks about his choices. At one point, after they recover Satan’s crown from a bottomless pit, Darkblood tells Mark that being a hero means believing people are worth saving.
These conversations help Mark find some peace. By the end of the episode, he returns to Earth and puts on his original blue and yellow costume for the first time in a long while, signaling that he is starting to feel like himself again.
Bruce Campbell Joins the Cast as Satan
Episode 4 marks the full debut of Satan, voiced by Bruce Campbell. Campbell is best known for playing Ash Williams in The Evil Dead franchise, making him a perfect fit for the horror-tinged storyline.
Satan is introduced in a weakened state after losing his crown to Volcanikka. Once Mark and Darkblood retrieve the crown, Satan transforms into his true form—The Great Beast—set to the heavy metal music of Slayer’s “Raining Blood.” Campbell’s performance balances authority with the dry humor he is known for.
New Characters Volcanikka and Domina Enter the Story
The episode introduces two significant new characters to the Invincible universe.
Indira Varma voices Volcanikka, the main antagonist of the episode. Varma is known for playing Ellaria Sand in Game of Thrones. Volcanikka is a powerful elemental warrior who controls magma and commands an army of Magmanites. She has taken control of Hell and plans to release the Vile onto Earth.
Kate Mulgrew voices Domina Darkblood, Damien’s sister. Mulgrew is famous for playing Captain Kathryn Janeway in Star Trek: Voyager and Red in Orange Is the New Black. Domina is an original character created for the animated series and does not appear in the comics.
William Clockwell Gets a New Voice
One change that viewers noticed in Episode 4 is the voice of William Clockwell, Mark’s best friend. The character returns for a scene where he talks with Atom Eve about her pregnancy. Longtime fans will hear a different voice, as Brandon Scott Jones has taken over the role.
Jones is known for playing Isaac Higgintoot in the CBS sitcom Ghosts and for his recurring role in The Good Place. He replaces Andrew Rannells, who voiced William since Season 1. As of the episode’s release, neither series creator Robert Kirkman nor Prime Video has provided an official explanation for the change. Scheduling conflicts are often the reason for such recasting.
The Post-Credits Scene Sets Up What Comes Next
As with many Invincible episodes, Episode 4 includes a scene after the credits. The post-credits scene shows Damien Darkblood climbing to the roof of a building on Earth.
Satan reaches out through their mental connection and asks Damien to investigate what Volcanikka was trying to do. Satan suggests that if she was trying to take over the surface, there might be something happening on Earth that threatens the Underrealm as well. The scene ends with Satan hinting that he may need to come to the surface himself.
The episode’s final moments also bring Omni-Man and Allen the Alien back to Earth, setting up a reunion between Mark and his father that will likely play out in the coming episodes.
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How to Watch Invincible Season 4
New episodes of Invincible Season 4 release every Wednesday on Prime Video. Episode 4 is available to stream now. The release schedule for the remaining episodes is as follows:
- Episode 5: April 1, 2026
- Episode 6: April 8, 2026
- Episode 7: April 15, 2026
- Episode 8: April 22, 2026
New episodes arrive at 12 a.m. PT / 3 a.m. ET on Prime Video. A Prime Video subscription is required to watch. The service costs $14.99 per month when included with an Amazon Prime membership, or $8.99 per month for the standalone streaming service.
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