Cool game you guys made! Spent a few hours on the demo, almost completed the upgrade tree haha. It's seriously addicting, congratulations on achieving it!
Few notes after playing:
I feel there is a bit of an genre identity mismatch. The game allows picking a random hammer at the start of a run, which leans into roguelite territory - there is no way to guarantee your favorite hammer(s) at the start of the run. At the same time, when a run is concluded, you can just "play again" and use the same hammer, which is the same as guaranteeing the hammer you already had. Which leads to behavior where a player may play and reset a run because the hammer they planned for wasn't available, but then when they get it, they just repeat the run many times with that hammer now guaranteed. I would suggest either making the hammer choice needed at every play including replays, or just let the player choose the hammer of their choice from the character screen and ditch the random element. If my 4 items are already stacking lightning damage, then of course I'd want my lightning hammer too, or if I'm farming coins I'm of course going to use the bonus coin hammers. The length of a game is so short that I personally feel the randomization is misplaced - there is no way to compensate for an "unlucky start". It would be different if the game length was longer and the other equippable items was also chosen during the game so a build identity could be established, reinforcing the roguelite element.
Generally the poison damage felt weak next to ghost hammer, lightning hammer and their respective ghosty and lightning-y upgrades in the tree. Since poison is a DoT exclusively, it really seems to fall behind as instant damage gets better and allows faster clearing. Maybe poison can stack or otherwise be a strong element when against difficult high HP enemies (bosses etc). Right now it doesnt seem worth the purchase. I suppose the strongest thing about poison is increasing damage from other sources, but that only makes the stronger lightning and ghost hammers even better.
The target dummy gets deleted if it is in the boss spawn location when the boss spawns. I'd suggest maybe make sure it cant spawn in that location. If I spent an item slot on the dummy then I feel it's weird that it just disappears.