This is neat, and reminds me of some old Flash games that I really liked back in the day. My only real complaints are that it's a little slow to get through each day - I find myself waiting for enemies to appear quite a bit - and that dying seems to send you right back to the start. It's nice in a way that you get to keep your upgrades, but it also compounds the issue of the slow-ish gameplay: you end up back on Day One but wildly overpowered, earning only a trickle of income, essentially waiting until enough enemies appear that you can continue upgrading the sandcastle. I'd rather just restart from the beginning of the day I died on. That said, that's a small detail for a jam game and this really is great fun overall. I hope it does well! I'd rate it highly myself if I were taking part in the jam.