Interesting concept. I was originally expecting each combination to do something more significantly different , but it was always fireballs. I didn't really understand until I was fighting the boss that the connections were just a quantity. I don't think which node you started with mattered. It played pretty well and was all together a good demo of an idea.

I really liked the spell drawing mechanic. Right now it does feel quite random, as it I feel little connection between the symbol I draw, and the effect created. Some of the effects, especially the ones where the fireball hangs in the air seem a bit weird. You  advise testing some patterns out in the beginning. If you want players to test things out, I would speed up the mana regen in the test room, so you don't have to wait between every attack you want to test out. The boss is quite lacklustre. Only a damage sponge that only walked around, and nothing else. It seemed also possible to kill it without it agroing onto you. One issue is that the game did not take into account different screen sizes. On my higher resolution screen, the game was placed in the corner. Try seeing if you can zoom it it, or have it at least centred. Good luck with your future endeavours.