Very well made game. I especially liked the lightning and the audio, the atmosphere just felt like we were in a cave. The shop system to go deeper actually makes it fit the theme a lot (we made a very similar kind of game). I liked it a lot but maybe you can add a cooldown for the bullets because I can grind more than 100 from a gold mine in like 5 seconds if I gitter click. Or an automatic shooting could be nice.