Great job with this game. I loved that there were 2 Characters. Tho the mage was waaay stronger!
On my first round I found the boss straight away and got demolished since I had no upgrades. Would have maybe been a good Idea to add a key so that you are forced to explore a little and not just stumble upon it.
Loved all the sound effects you added but you might want to modulate the pitch ever so slightly each time a sound is played especially when it's used often like the wizards shots. This helps with sound not becoming annoying.
Some more visual feedback when an enemy is hit would have been nice like a quick flash of the sprite or some slight camera shake. A boss health bar would also have gone a long way to help with player feedback! And maybe showing the tool tip of what you pick up as you pick it up so one does not have to hover over it to know what it is.
Overall a great execution and having it loop with harder? enemies was great! I enjoyed playing it a lot and got 3 clean runs in!