With “M3GAN 2.0,” the franchising of the 2022 sci-fi-horror mashup “M3GAN” suffers from sequelitis. At least it shows its symptoms clearly: inflammation and swelling. In the first film, Gemma (Allison Williams), a robotics engineer, becomes the guardian to her orphaned niece, Cady (Violet McGraw), and tests a new invention, the titular A.I.-powered robot-doll, on her. Cady grows attached to the responsive doll, which is programmed to protect the child and takes to the mission with a mechanical perfection, slaughtering anyone who expresses hostility—and does so with snarky pride in her absolute power. At its core, though, “M3GAN” (like the sequel, directed by Gerard Johnstone) is a family melodrama centered on Gemma’s struggles with parenting and Cady’s need to bond—plus the robot’s quick embrace of human cruelty. The film’s failures are painful because its setup is fruitful.

“M3GAN 2.0” heralds a genre shift from the start, with a title card that places the opening scene near the Turkish-Iranian border. There, an unidentified all-male plainclothes militia captures and shoots, at point-blank range, a female photographer who claims to be a tourist. Fear not: she’s not human but M3ganical in body and soul, rising back up to kill her way out of the ordeal and heedlessly slaughtering her captors and a person of interest to the U.S. government. At a secret defense-department conference in Palo Alto, her identity is revealed: she’s Amelia (properly, all caps, because the name is an acronym in which the M is for “military”), and one of her handlers, speaking into a mike, absurdly accuses her of disobeying orders.

The narrow programming of Amelia (played by Ivanna Sakhno) has made her as relentlessly amoral a killing machine as M3GAN proved to be in the first film; and, though Gemma is now an activist on behalf of rigorous international governmental control of the seemingly limitless powers of A.I., she comes under official suspicion of being the brains behind the rogue robot. In order to clear her name—and to save the world—she has to bring Amelia down. It turns out, in one of the many vague and facile plot points on which “M3GAN 2.0” depends, that the first movie’s monster, M3GAN, whom Gemma had apparently destroyed, has survived, and Gemma recruits her to take on Amelia.

As the geopolitical spectrum of the plot widens, the cast of characters swells to match. Along with the return of Cady and of Gemma’s scientific collaborators, Tess (Jen Van Epps) and Cole (Brian Jordan Alvarez), there’s the lead government agent, Tim Sattler (Timm Sharp), who keeps coming back for more punishment; Christian Bradley (Aristotle Athari), Gemma’s partner in activism whose first name is, pointedly, pronounced “Christián,” and whose craving for the spotlight hints at dark shadows; and yet another A.I. robot, a toylike miniature called (wait for it) Maxi. Best of all, there’s the scientist Alton Appleton, a wizard of neural-implant technology, played by Jemaine Clement, who gives his every clichéd line a wry, surprising twist—and who, despite his all-too-brief onscreen presence, dominates the movie to an unwarranted extent, because his device for silent and undetectable communication by thought alone plays a lopsidedly large role in the story.

In other words, the cast expands in order to assign faces to plot points, which expand in order to put the budget onscreen by way of large-scale action scenes. The movie features a frenzied car chase that reaches F1 speeds, a huge night-club-style dance party where M3GAN (again played by Amie Donald and voiced by Jenna Davis) gets to strut her stuff, and a riotous battle at a teeming A.I. convention. The sets include secret tunnels and hidden vaults, a concealed subterranean laboratory, and even a so-called vault within a vault that’s part of a massive research facility camouflaged in an innocuous low-tech business. (Best of all—yes, showcasing Clement again—are Alton’s finger-snap controls of the high-tech kinetic décor of his “Down with Love”-style high-income-bachelor pad.) And Gemma and her cohorts are forced to develop new technologically advanced gizmos in a hurry and repurpose items on the fly in order to do battle with enemies amid the snares and dangers of these elaborate settings.

The bombastic bloat of “M3GAN 2.0” brought to mind another misbegotten and overinflated sequel, “Ant-Man and the Wasp,” which tethered the most freewheelingly whimsical Marvel creation, the protagonist of the first “Ant-Man,” to the Marvel Cinematic Universe and expanded the story, the action, and the cast to match—and, in the process, dispelled the charm of the original. Yet, for all the stifling sense of boardroom-dominated creativity that afflicts even the best of the Marvel movies, these films also do the heavy lifting of developing a fantasy universe by giving the characters at least a modicum of definition in order to set the stakes of the action and personalize it, and by envisioning in some detail the technology, however ludicrous, that the superheroes’ powers depend on. In contrast, “M3GAN 2.0” is a shapeless grab bag of tones and genres that ramps up its stakes with A.I.-endowed robots wielding seemingly limitless powers that come close to comic-book superheroics, as when M3GAN returns from destruction or—in the moment where the movie definitively jumps the shark—leaps off a rocky bluff and flies, Superman-style, to her target.

The technology is the most interesting part of the sequel, but there’s both far too much hand-waving and far too little curiosity about the imaginative devices on which the film is centered. The screenplay (by Johnstone) perceptively touches on the core theme of “M3GAN”: namely, morality—the problem of a machine that simulates humanity without the ideas, intuitions, and emotions that complicate and moderate human behavior—and then leaves it merely touched on, again as a quick plot point rather than as a realm of experience for robots and their creators. This, too, becomes a matter of a device, which turns up all too conveniently, like much of the gadgetry in “M3GAN 2.0,” such as Gemma’s crash project to devise a mechanical hand with a human thermal profile—no time frame, no struggle, no problem.

Even the elaborate martial-arts-proximate combat, whether involving humans or robots, feels routine and underimagined. Comedic without being a comedy, camp-winking without being campy, sentimental without developing relationships, offering fight scenes without being an action film, replete with advanced technology yet hardly science fiction, very briefly grotesque without delivering horror—“M3GAN 2.0” has little dramatic shape and no directorial style. In striving for more than the original, it achieves far less. ♦