His super power is the ability to, as his name implies, remove his own arms, and his legs too for that matter.
While the character feels like somebody that DC Comics might have introduced in the 1960s, he actually first appeared in 1989.
Charles Murphy of the Murphy’s Law podcast is confirming a report from another podcast, which claimed Fillion would be playing the character named Floyd Belkin, otherwise known as Arm-Fall-Off-Boy.
This is the worst possible way to be defeated by somebody with superpowers.