It's always nice to see a fellow systematic game in this jam. The style is consistent, and the visual and audio quality are good.
Some critique on the design: It seems like once I got a good attack card, I can safely discard/sell the rest, since there isn't a limitation on how often a card can be used. Because of this, finding a new card feels less consequential.
After I find the boss, the game won't let me explore anymore. This feels unintuitive, since I would really want to explore more rooms to get more powerful cards and buy more upgrades to prepare for the bossfight. And because I don't have any control on when to find to boss, it also feels arbitrary. (Although I don't know if the player will always find the boss after a certain number of rooms; if that's the case, it will be nice to have a counter to communicate that)
Some nitpick: Seems like the blood elixir is used for healing, but the text on the card reads "DMG: 9d4". That really throws me off.
But overall great work!