I think the bosses need to drop more coins. I got to the third boss with no items because there was not enough coins to buy anything. I also think the slot machines are rigged.
This is a fun game. The bosses are not too difficult and it controls really well. I especially like how there is low cooldown for dashing. The art is fantastic, both the pixel art and the watercolor art. My feedback on the gameplay is that the wheel doesn't add much to the boss fight. I got by just fine without buying any items.
There was a bug for me when I defeated the second boss. The game thought I had lost and the retry screen popped up. When I clicked retry, I was on the last boss.