the Bionic arm is an invention that Susan and Marty built for Johnny to help him improve his dodgeball skills.
it can help whoever using it to shoot the balls with extra strength and speed. but it has a weakness and it's getting wet or if something gets stuck in its wires it'll Short circuit.
Johnny used it in Johnny Dodgeball to cheat, (hiding it under his sleeve) first beating Sissy, then Sissy accepted him to play with her as a team in a global dodge ball tournament, unluckily it got short circuited when a piece of cereal got stuck in before the last match. Johnny had no choice but to tell her the truth and apologized. then both of them worked as a team and with a help of the Test girls' dancing dress, they won the tournament.