Robot Monster Troopa
At the start of The Super Mario Bros. Super Show! episode "Koopenstein" the Robot Monster Troopa appears as little more than a background character, with Dr. Koopenstein wanting to obtain a brain for it, more specifically, Mario and Luigi's brains.
After their defeat at the hands of the Koopenstein Monster, a mindless beast that was once Dr. Koopenstein, Mario gets the idea to use the Robot Monster Troopa to defeat the Koopenstein Monster and rescue Princess Toadstool, who the creature had abducted. Getting into Dr. Koopenstein's old laboratory, Mario, using a remote control, activates the Robot Monster Troopa and proceeds to ride it up into the Swiss Cheese Alps with Luigi and Toad, both of whom are carrying Bomb Plants. By following the Koopenstein Monster's footprints, Mario manages to guide the Robot Monster Troopa to the Koopenstein Monster and Mouser's cave lair, where Princess Toadstool is being held captive.
Manipulating the Robot Monster Troopa, Mario has it engage in battle with the Koopenstein Monster, both of who end up in a stalemate, being equal in power. In an attempt to help the Koopenstein Monster, Mouser attempts to steal the Robot Monster Troopa's remote from Mario, but is stopped by Toad, who tackles Mouser to the ground, sending him skidding forward. Stopping behind the wrestling Robot Monster Troopa and Koopenstein Monster, Mouser can only watch as the Robot Monster Troopa accidentally steps on its own remote, electrocuting itself and the Koopenstein Monster. As electricity surges through them, both the Koopenstein Monster and Robot Monster Troopa, as well as Mouser, are sent tumbling off the Swiss Cheese Alps and into a river below. While Mouser and Dr. Koopenstein, having returned to normal and lost his memory of being the Koopenstein Monster, surfaced from this river, the Robot Monster Troopa didn't, and presumably sank to the river's bottom and perished.