These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
That One Puzzle: Many, usually overlapping with Guide Dang It. The clock puzzle, the observatory puzzle, decoding the alphabet cipher, decoding the number cipher, and all of the heart piece puzzles count.