Best puzzles of 2018 Q4 (October - December)?

Question

This question is part of the best-puzzle award series.

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What are your nominations for the best puzzles, here on Puzzling.SE, of the fourth quarter ( October / November / December ) 2018?

Suggested guidelines for nomination:

• Nominate each individual puzzle in a separate answer, so they can be upvoted/downvoted separately.

• No more than 3 nominations per person.

• Don't nominate your own puzzles.

• Before you nominate a puzzle, check to see if someone else has already nominated it. If they have, then add to that nomination as a comment (or edit it) instead of nominating the same puzzle again.

• In your nomination, explain what it is that (in your opinion) makes the nominated puzzle such a good one.

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Some lists to help jog your memory (your nomination doesn't have to be from these lists):

• Algorithmically selected "best of":
  • Popular puzzles, both in score and in vote to view ratio, from 2018 Q4
  • Well received puzzles you may have missed from 2018 Q4
• Best by votes/views:
  • Questions with the most votes from 2018 Q4
  • Questions with the most views from 2018 Q4
  • Questions with the highest-voted answers from 2018 Q4

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_{Meta-meta issues:}

• _{Is this kind of thing allowed on SE?}

  • _{Yes, Photography SE and Sci-fi/Fantasy SE do something very similar.}

• _{What's the point?}

  • _{To highlight and encourage good practice in a way that goes beyond upvotes.}
  • _{To work towards building a 'hall of fame' of some of the best puzzles on the site (perhaps to reside on a future puzzling.SE blog) - think of it as our 'greatest hits album'.}
  • _{To prompt members to put forward their own reflections on what makes a high-quality puzzle.}

Answer 1

The Two-Trench Truce by Level 51

In the words of ManyPinkHats who solved it:

That is a very impressive amount of content to fit in such a tiny cryptic.

This is one of those puzzles that, even upon seeing the solution, I look at and still wonder how the creator actually went about crafting it. Multiple layers of moving parts all crammed into a tiny package make for an impressive effort from a purely technical perspective. However, add to that a thematic consistency and conclusion that makes you smile and you've got a truly great puzzle.

Answer 2

lolcatz can haz ur infinit cheeseboard by deep thought

User deep thought took a chess board, expanded it into infinity, and added one (1) chess piece with extraordinarily clever (if somewhat complicated) movement rules.

The result? A chess problem that the entire humankind (well, at least, all the mathematicians) would applaud if ever solved.

Answer 3

Which movie will we watch? by formica

I spent a ton of time on (and really enjoyed) this puzzle.

I think it was quite simple and elegant in its construction, but still managed to stump the majority of the community for a significant amount of time, even with the 5.5 clues provided by the OP