The Legion of Super-Heroes comics have a recurring gag where the members interview potential new members that have moronic powers or an inability to use them correctly. One of these rejects is Arm Fall Off Boy.
Arm Fall Off Boy's origin is unknown. Matter-Eater Lad claimed Arm Fall Off Boy got his power by holding onto the anti-gravity Element 152 (which, based atomic mass given, should be Europium) too long. However, he may have been joking. As you probably guessed from the intro, Arm Fall Off Boy tried to join the Legion and failed.
In the Zero Hour timeline, his real name is Floyd Belkin and goes under the name Splitter. It is also stated he from the planet of Lallor, making Matter-Eater Lad's claim seem more plausible since most of the planet's inhabitants are normal people. In Legionnaires #43, he tried out for the Legion and was among of the finalists. However, he was rejected for literally falling apart during the last test. Later, he was seen as a member of the Heroes of Lallor (Lallor's main superhero team).
Arm Fall Off Boy easily has one of the dumbest powers ever. He can detach his limbs, which seem to harden, and use them as clubs. He can reattach them as well. Unlike the M. F. Enterprises Captain Marvel, he cannot fire him like a missile and has to use his other arm.
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