The entire advanced mathematics. Go sufficiently far and mundane matrix multiplication will look like daemonic sigils. Write out a moderately complex math proof and you’re essentially commanding inhuman tongue. Then when you convince them that it’s really not devil summon spell you can tell the old era folks, that all these symbols is why the sun rises as fast as it does and moon has phases.

True, but there are way better fammade 5e implementations of the MtG worlds. Not sure if they already got to Capenna, but I’ve seen Kamigawa and Innistrad and honestly stuff looks like WotC made it themselves. Will post links when I find them tomorrow