Actually, I think the joke works better if it’s his left hand. I’m right-handed, so if I lost my right arm, I’d be pretty pissed. Having him reveal he is left-handed is unexpected and subverts the reader’s expectations (assuming most readers are right-handed). You could further layer the joke by having the yellow-haired character pop out and zap off his left arm. And if you REALLY wanted to layer the joke even further, you could have him reveal that he didn’t even need any of his arms to use magic (like his feet or his head, or his… ).
Still, this is a very cute comic and I like your simple style.
Lol, is it ok if I yoink the idea I just came up with? It would make for a good Totally Accurate Arcane chapter.