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The DC calculations for blind fight are absolutely off. Also, there seems to be some other, hidden, unlisted requirement you need to meet to pick blind fight?
Steps to reproduce
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Be a swashbuckler, have 90 bluff, use dirty fighting, which should result in 10 + 1/3 character level (30/3, so 10) + 1/6 bluff score (90/6, so 15), so 35
Expected result
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DC 35
Actual result
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DC 43
Screenshot(s)
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Notes
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The build is a 21/6/3 swash/fighter/bard. Dex-based.