To make it not seem boring but funny turn him into an actual one armed right handed man who got his left arm got eaten by a shark.
Since two punch man is a fraud why not one punch man with only one arm to land jabs and punches, and to make it more entertaining this guy have to come back to boxing even though he only has one hand and an arm. Why not? Because he still has a dream and that is boxing, and its not always too late to always try and be succesful.
Yeah not the gag bald headed character with
overpowered punch that can one-shot anyone. But a boxer who realised his dreams late after becoming one armed right handed. And yeah he is gonna fulfill his dreams.