It took me an incredible amount of time to win wave 10. I thought I had won but NO ten more levels! And one of your comment said that you made 100 waves. You really need to change some things so it gets easier because otherwise this is going to be the next dark souls :P I got really tired with my left little finger(I shot with left ctrl) so after awhile I started to use the right hand to shoot(still with left ctrl though, It looked weird). That's how long I played. I really like the art for the player and the enemies. I think you could make the ground look gooder but that is just my opinion. The movement was nice and so was the shooting. Because the game was so hard I had to come up with different strategies and ways to win waves but sometimes they surrounded you and it was impossible. I like that you could jump over the hole in the bottom part of the first level but that it was hard to do. The music was also nice even though you did not make it.
I have a question. Do you restart the scene when you die? Because if I die when bullets were in the air they are still there when I spawn, same thing with coins. If you don't want to restart the scene because you will loose the gold variable and upgrades your character has you can have something called a gamemanager which can store variables between scenes.
Things to improve: The bonus round has a timer on 15 seconds but after the timer the gold is still there, I think that the gold should go away if you didn't pick up every gold. When the monster fall down the hole they get back on the top, I think the same should happen with gold if it falls down the hole. Make the game easier :D I found a bug where sometimes when you died you did not get the upgrade menu.
The most frustrating bug I found was when I tried to save up some gold to be able to buy upgrades later. I got over 1000 gold but when I died my gold resetted :(
Here is a link with a video on the issue, maybe you can get some info on what happened from the video so you can fix the bug/glitch. https://streamable.com/ur4bz
Overall it was a great game, I think you will get a good spot on this gamejam!