Arm Fall Off Boy has the ability to detach his own limbs, which he can then use as blunt weapons. Matter-Eater Lad claims he gained his powers through carelessness while holding the anti-gravity metal Element 152, but he may not have been serious. In his introduction, he is an applicant at the first Legion tryout, and the first Legion reject.
Major Story Arcs
Following the Zero Hour reboot, the character appears again and is identified as Floyd Belkin of the planet Lallor. Under the name Splitter, Floyd participates in the Legion's tryouts and is one of five finalists, but he is denied Legion membership after he panics and literally falls apart during the last test. Later, he appears as a member of the Heroes of Lallor.
In the Legion of Superheroes in the 31st Century continuity, Floyd had a whole issue devoted to him. It is shown that his arm first fell off shortly after he was born, much to the alarm of his parents. He grows up wanting to join the Legion and meet Phantom Girl, and eventually travels to Earth to do so. Once there he saves the Legion from the menace of Starfinger. The Legion tell Floyd that Legion tryouts are still a few months away, but Phantom Girl lets Floyd try on her flight ring to see what it's like. Unfortunately the ring flies off with Floyd's arm . . . only his arm. Undeterred, Floyd returns home excited about the adventure he just had and looking forward to the next Legion tryouts.
Floyd has received the dubious honor of being one of DC's most ridiculous creations (though he was meant to be), and even got a media mention in July of 2010 in Late Night Liars.
The Suicide Squad (2021)
In this movie, he's called TDK (The Detachable Kid). He's a member of the first team. The character is portrayed by Nathan Fillion.