Love the main menu, super clean. The pixel art is crisp and the color palette chosen for the field is really beautiful. With the music playing, I could totally see myself zoning out and just grinding this for way longer than I planned to.
"Try your best" being the only instruction made me laugh. I knew immediately what kind of experience I was in for. But honestly, you communicate the gameplay well through visuals and the HUD, so it works.
One small thing I noticed, when I restarted, the castle visually reset to level one, but the upgrade cost didn't. It was still priced like I already upgraded it once. Not sure if that's intentional, just figured I'd mention it in case.
Other than that though, this is the kind of game I could easily sink time into. Really nice job.