They get extremely hard at the end. After spending 30 minutes on level 10, I had a large table of good and bad tiles, but I never guessed the answer was THAT table. Skipped level 11 quickly by luck, with a different rule in mind. Couldn't guess the rule for that level.
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Yes, some people also told me that they sometimes luckily managed to skip a stage without discovering the rule. It's perfectly possible, since there's more than just one path available, and there are valid blocks even outside the path, also to add randomness and multiple options.
Thank you so much for trying it. I'm happy when people play my game, especially when they reach the final levels.