No problem, I'm glad to hear that I'm not just incredibly bad at the game, but it is actually a bit unbalanced :D
I think I know what upgrade you're talking about, I went from doing about 50 damage a shot to doing 800 damage a shot out of the blue... That took me by surprise. Also, by wave 7, something strange happened. I don't know exactly why, but suddenly, everything disappeared. All the monsters, my upgrades, everything. Then they started raining down again, only now I wasn't doing damage at all... My elephant was also gone, and the only thing doing damage now was my flames and my missiles (and they were only doing like 1-3 damage?) Maybe too many monsters had spawned and it basically soft-crashed?
I could see some boss fights being a really cool addition! I hope you keep iterating on this, you're off to such a great start. One of the best games I've played this jam for sure! :D