Since the monster arm episode I said it'll play a bigger role later, and I still think that. Maybe the monster arm became like the inner demon of Marco and it gets "activated" when he has really strong feelings, e.g. rage. And I have the theory that Marco is somehow connected to Toffee or to the septarians in general Idk. I have the feeling that there will be a huge plot twist about Marco. Who knows maybe he's a real butterfly, or maybe he's related to toffee or something completely different Idk, what do you guys think?
Credits to me btw