Reuse: Solution

Each of the nine clues refers to some part of one of the other nine puzzles. They are given sorted alphabetically by clue, not by puzzle. To avoid accidental spoilers, these parts are linked below both by the clues in this puzzle they correspond to and by other puzzle (however, clicking on the link for a part will tell you both the clue and the puzzle it corresponds to).

• Alligator pear (7)
• Before the r extracted from the last word
• Every other column of 8x8
• First note of the anhemitonic audio file
• In the last three but not in the first four
• Red 246
• The number of occurrences of e, out of 39
• The operation that z represents
• Top left of 8371

• Nothing Is Forever
• Spot the Difference
• Every Word Is Three Letters
• Night Sky
• Compound Words
• Leftovers
• What Does It Mean?
• Another Angle
• When and Where

Some of these clues may help solvers solve some of the other puzzles, especially as they solve more puzzles and can start trying to determine which clue applies to which other puzzle.

How to get the answer (minor spoilers for all the links above, which is why it's on its own page)

Answer: second

Note: In Nothing Is Forever, Every Word Is Three Letters, Leftovers, Compound Words, and When and Where, there were no changes to the puzzle needed to get the clue. (In all of the above but When and Where, it is not that surprising that this was possible.) In Spot the Difference and Night Sky, the clue was explicitly inserted into the puzzle in the puzzle design process. In What Does It Mean? and Another Angle, the clue was kept in mind during puzzle creation but didn't constrain the puzzle that much.