Made it to day 35 on my last run and discovered something interesting which doubles as the best anti-cheat. It appears the enemies get boosted based on your total levels/upgrades, which isn't much unless you do something stupid like cheating and give yourself infinite castle levels perk then buy castles until you're dealing 9 million a shot. This of course leads to the enemies killing you before the first shot even lands by day 33 and ending the run on day 35. good times XD
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I kinda hope this was intentional as that would be funny to me. Other than that, it's actually a really fun game and I look forward to more content.