Genre challenges ask for titles from a single genre, with requirements built around its tags and subgenres. Easy, Normal and Hard modes are worth 1 point each and stack, so finishing Hard earns all three.
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Mastery is a separate second run of the same challenge worth 4 points. Titles usually need a minimum runtime of 30 minutes, which rules out most shorts and music videos.
Tip. Easy mode commonly accepts titles you finished before joining, so start by matching your existing list against the requirements.