Two Years Earlier
An unnamed wrestler loses a match against a helmeted gorilla in a jungle arena. As the man goes to a nearby river for water, he is inadvertently exposed to toxic wastes and discovers that he can merge any two animals together, giving them the abilities of both. Also gifted with superior strength and agility, the man returns to the arena and defeats the gorilla, and takes its helmet as a trophy. Donning it, the wrestler becomes... B'wana Beast.
Faceless Hunter has taken B'wana Beast to his spaceship in orbit around Earth and imprisoned him within a power-manipulation device. The alien tells B'wana Beast that he wants to unleash his true potential, and then activates the device, causing the hero to scream in agony.
In Star City, the Green Lanterns take away Starro while the heroes collect the inert drones and make sure everyone is uncontaminated. The only two heroes still missing are Aquaman and B'wana Beast. Batman tells the assembled heroes that Faceless Hunter captured B'wana Beast, but they can't rescue him until they secure the Earth.
Aboard the spaceship, B'wana Beast wonders why Faceless Hunter is still a villain when his master has been defeated. The alien informs B'wana Beast that he was a hunter on a planet of pacifists, and he willingly joined forces with Starro to destroy his homeworld. Now he plans to use B'wana Beast's power to become the most powerful villain in the universe. The hero breaks free but his strength and agility ultimately prove useless against Faceless Hunter's superior weaponry.
Captain Marvel spots Aquaman standing on the pier, facing out to the ocean. The King of the Sea turns around and reveals there is a drone on his face. Batman tries to remove it but Aquaman throws him off the pier. The other heroes are unable to subdue Aquaman, but Batman tasers him unconscious.
Faceless Hunter returns B'wana Beast to the device and tells him that he is unworthy of his powers. Instead, the alien will use his powers to hunt planets throughout the universe.
Batman informs the heroes that it's time to free B'wana Beast. However, before they can proceed, the drones suddenly start forming into one massive humanoid creature. Batman realizes that Faceless Hunter is using B'wana Beast's amplified power to merge thousands of the drones simultaneously. Captain Marvel launches an attack and attempts to overload it with his mystic lightning. The creature grows larger and then blasts Captain Marvel with an eyebeam. It then claps its hands together, setting off a resonance wave that echoes through a nearby radio tower. Batman warns the other heroes that the creature plans to generate a seismic wave through the tower and others and destroy Star City, and the entire seacoast.
The heroes attack the gigantic creature but discover that it can siphon their powers at will, leaving them as aged husks. It sets off the second of three radio towers and Skeets warns Batman and Booster gold that they're out of time. Firestorm tries to overfeed it but fails just a Captain Marvel did, and Batman informs Booster Gold that he's their only hope.
Skeets teleports Booster Gold to Doc Magnus' lab. The Metal Men are immune to the creature's power drain, and their only remaining hope. However, Booster Gold discovers that Magnus has been possessed by a Starro drone. Magnus unleashes the reprogrammed Metal Men against Booster Gold, who tells Skeets to try and communicate with the robots.
The Star Conqueror marches across the planet, draining away the energy of anyone who opposes it. Batman himself goes down. However, Booster Gold arrives with the Metal Men, who Skeets has successfully reprogrammed. The robots merge into a jet fighter and attack the creature, while Batman says that he'll have to find B'wana Beast and remove him from the device to stop the Star Conqueror for good.
As Batman flies into space using his Batrocket, Faceless Hunter detects his approach and opens fire. Batman is unable to successfully counterattack as the spaceship is protected by a forcefield. The Caped Crusade fires one last barrage of missiles, which embed themselves in the forcefield. Faceless Hunter then destroys the Batrocket and turns back to B'wana Beast. The alien is unaware that Batman hid himself in one of the missiles, and crawls out of the front end to get to the spaceship. However, Faceless Hunter detects Batman when he enters and attacks.
The Star Conqueror manages to split the Metal Men apart, but they quickly regenerate and then merge into a single gigantic humanoid robot, Alloy.
Faceless Hunter strips Batman of his battle armor and captures him in a portable forcefield. The alien admits that Batman is a worthy foe and prepares to cut off his head as a sign of respect.
The Star Conqueror grapples with Alloy, twists it into a gigantic metal power, and then uses it as the third tuning fork.
Batman manages to break free of the forcefield prison and grabs one of Faceless Hunter's forcefield projectors. He traps his opponent inside and goes to B'wana Beast. B'wana Beast says that he can control the Star Conqueror if he gets close enough, and Batman flies the spaceship down toward the planet. Focusing all of his might, B'wana Beast forces the creature to break apart into his separate parts. However, the effort is too much and he's disintegrated. However, before he dies, B'wana Beast tells Batman to tell Vixen that he loves her.
Batman flies down as the Metal Men recover, and Vixen realizes what has happened to her fiancé.
Later, the heroes gather at a cemetery to honor their fallen comrade, who gave his life to save their planet.