Nice! I can see a lot of work went into this one! Lots of pixel art and it's pretty good! I liked the music at first but it started to wear on me, it would be good to mix it up more, or make it more ambient.
I figured out the basics of how to play right away, but not sure about advanced strategy. I'm a big fan of slay the spire and mtg but not sure how this translates.
Some thoughts. - Just use left mouse button for everything. I'm pressing enter, space, right mouse, but there's no need! - It would help if it showed what spells do when you mouse over them. Maybe even apply that to everything (enemies, bars, etc) - Cool idea to put the text sideways but it's hard to read!
A great first entry, congrats!
Next time my advice is to simplify! Think about how the game would be better if it had less stuff that was just better balanced and polished. For example instead of 6 spells maybe have 3. Instead of an upgrade system maybe don't have that at all or simplify it and make it more interesting choice. Like choosing a new card for your deck.