Well? First of all thank you very much for pointing that out. However, I would like to say that it's very, very tough to draw a simple hard *objective* line on this topic; or any art or fiction really. In any fiction, the moment you put a hard definition, people will always find a way to subvert it XP
The last definition of "Magical" was meant to fit a certain Magical Girl show I heard where the Magical Girls were actually mecha but they barely look like mechs and look closer to Magical Girls, and the author clearly intends it to look kinda Magical.
In what you say about replacing Metroid main char ability with Magical Power, you only made a sentence to pass the premise as "makes sense". "Makes sense" is kinda subjective, but if you actually imagine it, I think the Magical explanation would seem ad hoc imo; and hence it won't really make sense.
Do you have better suggestions for the criteria? It will be very helpful if you can provide better criteria. For now, I will add that "the author implicitly intends the power to look Magical" as a band aid fix.
P.S. the rule is meant to be very loose though to give jammers the freedom to subvert the genre. In general wizards aren't considered Magical Girls either but I decided to allow it for the purpose of this jam for example.
P.S.2: Regarding the part where you quoted from the "What is a Magical Girl" section, I also would like to stress that those are just examples, and not part of the rules.