As a roguelite fan, I really liked this and I think at a certain point I lost track of time while playing it! It clearly needs polish but I think the mechanics are already quite solid for a jam!
I read you'll keep working on it, so I wanted to tell you to pay attention to the balancing of the upgrades. Specifically the +1 discard, I think it can be really rapidly broken since you can have so many discards (I think in the end I had 13) that you can simply create a chain of cards and discard your full starting hand in one round, I rarely saw the opponent play. I think it might be balanced by making it less probable of an upgrade, by creating more types of cards (more types of cards -> less probability to chain the whole hand), maybe making the starting hand bigger as the game goes on or even just making the two players start alternating (So you can't destroy him in one turn).
But I want to make my point clear, it's a really good vertical slice! I'll check on it in the next weeks to see how you keep iterating it! Great job!