Twenty years ago, Marvel hired “The Walking Dead” co-creator Robert Kirkman to write “Marvel Zombies,” a five issue mini-series set in an alternate Earth where the 616 universe was overrun by a plague of the undead. It was hugely successful and spawned a litany of crossovers, including an appearance by Ash from “Evil Dead.” Now, Disney+ has released a four episode mini-series “event” that borrows that project’s name, but won’t follow the comics for its narrative. Instead, the show spins off of the zombie-infected “What If…?” episode, expanding on that world’s lore for something a little different than its source material.

This event plays out like an alternative “Avengers” tentpole — a variation of how “Avengers: Endgame” could have turned out if the playing field had been heavily reconstructed by the presence of brain-eating walkers, and pervaded through the MCU’s plans to pay off the “Infinity Saga.” If you’ve followed any of Marvel’s other Disney+ animation efforts, you have a pretty strong indication of tone and quality (for better and for worse), but you may not be entirely prepared to see that TV-MA rating get put to good use and how much blood gets spilled across its two-ish hour runtime. It’s just a bummer it doesn’t offer much more than that.

The only recap you’ll need to get caught up before “Marvel Zombies” is housed within the “What If…Zombies?” episode. “Marvel: Zombies” opens with the next generation of heroes — Kate Bishop (Hailee Stanfield), Kamala Khan (Iman Vellani), and Riri Williams (Dominique Thorne) — as they try to navigate the post-apocalyptic wasteland their world has become. Accompanied by a teddy bear-headed Iron Man (Tony Stark’s decapitated body in his suit, powered by F.R.I.D.A.Y.), they go on supply runs and try not to be eaten or turned by a local horde of zombies led by an undead Clint Barton. 

But the trio comes into possession of the show’s MacGuffin, a complex tech device shrunken by Pym Particles into a bite size doodad. Convinced it’s the key to saving this world, they embark on a journey that takes us across this transformed landscape and into content with a number of other survivors, from Shang-Chi (Simu Liu) to Alexei (David Harbour) and other surprises. The general shape of the plot follows the same structure as most zombie stories of the last 20 years, but the action is the main attraction here.

The second episode opens up with a slick sequence that looks like a “oner,” while every other episode features at least one big fight scene where zombies are sliced into pieces, riddled with bullets, or otherwise rendered asunder in bloody, grisly fashion. It’s enough of a departure from Marvel’s recent animated fare to feel thrilling and new. There are exciting uses of pre-existing mythology grafted onto this new conundrum, like seeing Red Room mind control tech put to use controlling a crowd of zombies. But most of the project’s magic comes from seeing all these familiar characters and the ways this world-gone-bad have transformed them into something new entirely.

Perhaps the biggest of those supporting appearances? Blade! He’s never made an appearance in the MCU proper outside of that post-credits from “The Eternals,” but here he’s a big force, having taken over as the Fist of Khonshu from a slain Moon Knight. The treat of seeing him in action and basically reduced to his simplest form, Cool Guy With A Sword, makes it doubley depressing that they never got a live action take with Mahershala Ali sorted out. Blade is voiced here, by Todd Williams, which brings us to some issues.

As much as this event requires the viewer to invest in an alternate version of the MCU, there’s so much inconsistency in the vocal performances. This plagued “What If…?” as well, because it’s distracting to try to parse when you’re hearing the actors who originated the role or well-meaning soundalikes. Iman Vellani and Florence Pugh do pretty exemplary work here, but there doesn’t always seem to be as much rhyme or reason for the glaring omissions either, outside of pay or availability. Kerry Condon returns to voice F.R.I.D.A.Y., but Rachel Weisz doesn’t return to voice Melina Vostokoff? Paul Rudd is heard, but not Chris Hemsworth, who will appear in literally any commercial imaginable? F. Murray Abraham had time for this but Tom Holland didn’t? (Hudson Thames voices Peter Parker again, as he did in “Your Friendly Neighborhood Spider-Man,” which we also reviewed.)

Additionally, the alternate timeline feels murky at different points. There’s a five year jump in Shang Chi’s strand of the narrative that mirrors the blip, but it implies that his big screen origin is sped-up by the zombopcalypse, though other characters feel further along in their journeys than they should be without similar circumstances. However, that feels like a minor complaint compared to the issues with the series’ tone. “Deadpool & Wolverine” scribe Zeb Wells is the main writer here and his particular penchant for comedy is on display — there’s a sequence that broadly homages “Mad Max” that features a random Journey needle drop — but he squares it with the story’s pathos less effectively than he has in his last few years writing the “Amazing Spider-Man” comic series. 

Ultimately, it is difficult to feel compelled by any of the drama at hand. These aren’t “really” the characters we know and love, and as more and more drop like flies for dramatic effect and easy tear jerker moments, the format becomes see-through. It’s four serialized episodes with cliffhangers, but collectively it feels less like a mini-series or an event and more like a throwaway telefilm. Adding that the animation style still skews to an ugly and cheap feeling aesthetic, “Marvel Zombies” is fun, but in a passing, forgettable sort of way.

“Marvel Zombies” premieres on Disney+ on September 24.