Permanently losing units between waves is a very interesting choice, and I like that it forces you to choose upgrades that give short-term benefits instead of investing everything into money generation. However, I think balance-wise it’d maybe benefit from being able to buy new units over and over up to a limit so that you can’t softlock by losing everyone in one battle. I’m not sure if the cogwheel in the corner is a debugger menu or an actual aspect of the game, but the Restart Battle option in that menu does not return any units that died in the previous attempt as well.