"The Brain Buster" is the thirty-ninth episode of the first season of Justice League Action. It is the overall thirty-ninth episode of the series.
A mysterious creature abducts Batman, Mr. Terrific, Lex Luthor, Calculator, and Brain to put them to the test to discover the smartest among them.
At Belle Reve, a prison patrolled by hovering drones, the external defenses activate and open fire on an incoming object in the sky. The shots bounce off and it bursts through the wall of the prison building to reveal itself as a robot with wheels instead of feet. It passes along a corridor looking for a particular prisoner in the cells. After rejecting Edward Nigma and Gorilla Grodd it settles on Lex Luthor and tears down the cell door. As Luthor picks up a device used to play chess, the robot takes hold of him, makes off, pursued by the drones and, at the end of a corridor, enters a travel portal and disappears.
Later, in the Watchtower, Batman and Mister Terrific watch video footage of the abduction together with that for similar abductions of Calculator and The Brain. Unable to determine who is responsible, they are about to leave to find out when a portal opens and the robot enters. It identifies the two superheroes as its targets and a fight ensues. Mister Terrific is hit by a beam from the robot's head and is transported to where the three abducted villains are held captive. As Luthor complains about the company he has to keep, Batman also appears as the fifth prisoner.
Standing on a ledge in a barren, rocky landscape with a multi-colored, alien sky, they hear an imposing voice tell them that each has been chosen for their great intelligence - the voice is only represented visually by a large pair of spectacles floating in the air and edged with flames. The five are told that they will have to compete in games to determine who has the greatest mind and that the losers will be obliterated. First, they are placed in gliding vehicles on a racetrack each with a spherical Rubik's cube which they have to solve to get going. Racing around the track, each tries dirty tricks to beat the others. Nearing the finish line, Calculator forces The Brain off the track so that it is eliminated. The voice decides to humiliate the losers in floating transparent boxes before disposing of them.
Next, the remaining four are standing on floating blue discs and are told that two have to reach the discs which change red occasionally. Batman reaches one by causing Calculator to fall so the latter is placed in a box. Luthor makes his chess-playing device into a gun and shoots at Mister Terrific. The latter is about to reach a red disc but instead decides to attack the big spectacles accompanied by his T-spheres and fails so goes to a box less his spheres. Luthor stands on a red disc instead. He and Batman are moved to a giant chessboard and have to move the pieces in a game while a jet drone shoots at them to hurry them up. Luthor uses his gun to gain advantage and gets checkmate, sending Batman to a box.
Expecting a great reward, Luthor is instead gripped from behind by the robot and has a helmet placed on his head. The voice now materialises as Mister Mind, a small caterpillar-like creature with large spectacles that speaks through a voice box on his chest. Wearing a similar helmet, he says that he intends to transfer his mind into Luthor to take control of his great brain. Suddenly, however, a T-sphere intervenes and stops the transfer process. Mister Terrific had been left with the T-sphere that goes flat across his face as his mask and had used it to hack and open his box and that of Batman. The robot attacks but the superheroes dispose of it and capture Mister Mind. Batman smugly tells Luthor that he had been using him to discover Mister Mind's plan.
Appearing in "The Brain Buster"