This felt really ambitious for a game jam, but you made a solid MVP and it was pretty fun! I really liked the Mega Man-esque mechanic of getting a new passive bonus with each metal completed. There was some nice variety in abilities there and it felt really rewarding to see each new bonus.
I feel like the autobattling mechanics were a bit hard to follow, maybe partially because of a lack of animations. I think I mostly understood it, but only by reading the description. If I was just playing the game, I don't think I would have totally grasped how the battles worked. I also wasn't sure why you'd want to buy the larger deck upgrade. Normally in deck builders you want a smaller deck so that you're drawing your best cards more often, so the benefit of a larger deck wasn't clear to me (and I didn't buy it), but I may be missing something there.
I think I very unintentionally stumbled into the OP strategy of having a deck with mostly defense cards and a few attacks. Although the battles were a little slow, roughly the last 2/3 of the game were a breeze. For a while I was only taking damage the first couple turns of a battle and by the end I was getting through completely unscathed. I ended the final alchemist battle with a whopping 269 armor! Maybe it would make sense to use something like the Slay the Spire mechanic of losing your armor each turn? That would at least make it more likely for an enemy to occasionally get through the armor.
Nice job! 😊