[@TheUnknowable]

So I've given some thought as to which villain could have taken Roy's arm. Captain Boomerang isn't a bad fit, if we're assuming he's using boomerangs of exaggerated sharpness and the like. The other option is to go with one of Green Arrow's rogues, since they would likely have the most motivation to want to make Roy and/or Oliver suffer, and the one who comes to mind is Merlyn.

Any thoughts or suggestions from anyone?