I had thought up a great medium to replace Metal. Metal really should be a part of Earth anyway, but I broke it out because I could only think of 11 mediums and I needed 1 more. I thought of a great solution, but then... I forgot it. It has eluded me for over a week now. But something about Quibish's comment a few hours ago brought it back, even though he never mentioned anything similar to my solution, he just knocked Metal a bit. So thanks Quibish for accidentally doing that!
Metal has been rolled into Earth and replaced with Holy. Holy is flexible in that it allows lightning and holy avenger stuff. So that's awesome. Can't believe I forgot that shit for a week.
Okay, here is a much more elaborate piece than what I posted a few hours ago. I am now illustrating how the magical pairings work, with three examples that I think serve to reinforce the concepts.
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In my view, one of the key purposes to graphic design like this is to teach the rules in a way that can almost be learned without the text. I think you could almost hand someone just this page, and they could pretty much see how the magic system works. I think that is a pretty damn nice feature. If anyone has suggestions to improve it, I would love to hear them.