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In chess, the white player makes the first move.
It is generally understood that this gives white a minor advantage, with a win rate of 52-56%.

In this initial position, white actually has checkmate in one move!
    

However, the player who makes the first move doesn't necessarily have the advantage...
Can you find an initial position where black's pieces still mirror white's, but black always wins?

Challenge

Rearrange all the pieces on a standard chessboard, maintaining symmetry, such that black can force checkmate.

Conditions:

  • Black's pieces still mirror white's pieces.
  • No pieces on the opponent's half.
  • No pawns on the first rank (row).
  • All standard pieces must be on the board. No more, no less!
  • White to play first, but black has checkmate in x moves.

Extra!

Bass has posted the first solution! It's not the solution I found and uses a slightly different approach. So, to make it more unique I would like to add a further challenge:

  • Find the position resulting in the fastest possible forced mate.

Notes and hints:

  • The bishops can be on the same colour squares.
  • I've found the board editor on lichess.org very useful for finding a solution:
    • The position shown at the top of this puzzle is here.
    • Use the "Analysis Board" with stockfish turned on to check your solution. If it shows you #-1, #-2 etc. then you've forced a black checkmate!
  • There may not be one unique solution. I was unable to find any other solutions in several hours, but I found the premise interesting, and the puzzle was challenging.
  • I hope it's fun to solve! I've not been able to find information about a puzzle like this online, so it's possible I've missed something obvious. These hints are based on how I worked out my solution, but let me know if there's something wrong!
  • Hint 1:

    Try to restrict the moves that white can make! If white has a choice, they will choose the move that doesn't lead to checkmate.

  • Hint 2:

    Try to block almost every piece in, especially the king. Test out various scenarios without worrying about piece restrictions, and check your strategy works!

  • Hint 3:

    White and black initially have the same moves available to them. If black could deliver checkmate, white could do so first! So, white must be forced to make a move which opens up additional possibilities for black.

  • Hint 4:

    The only 3 ways black can get additional movement options are if:
    1) A black piece becomes unpinned
    2) White puts a piece in front of an attacking pawn
    3) White captures a black piece that was blocking something.

  • Hint 5:

    Forcing white to sacrifice a piece to a black pawn is important - it allows black to make a capture move that was not available to white. Use this pawn movement to your advantage!

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  • $\begingroup$ Why did you post so many hints at once? We generally post one hint at a time after a few days if no one could solve the puzzle. $\endgroup$
    – melfnt
    Dec 19 '20 at 22:18
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    $\begingroup$ Ah, sorry! I haven't posted much here before, so I'm not familiar with how things usually work. I put them there so people have the choice of whether they want to stick at it or get a bit of a nudge in the right direction. I'll remove them for now, but I'll reinstate them later even if someone solves it. $\endgroup$ Dec 19 '20 at 22:27
  • $\begingroup$ I've added an extra challenge to the puzzle. I'm sorry to Bass who already posted an answer - you showed there are probably many more solutions than I realised! The additional goal should make the puzzle have a more narrow set of solutions. $\endgroup$ Dec 20 '20 at 0:07
  • $\begingroup$ It's not a big deal anyway, happy puzzling! $\endgroup$
    – melfnt
    Dec 20 '20 at 9:59
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This should do it:

enter image description here

White is in zugzwang, so black has

a mate in 5 with by underpromoting to a knight on g1.

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  • $\begingroup$ Oh, interesting! That's not the way I did it, but it's a really good solution. It's actually possible to get mate in one, so for anyone looking for an extra challenge, do try to find that as well. $\endgroup$ Dec 19 '20 at 23:11
  • $\begingroup$ @DanielCausebrook Well, two half-moves. $\endgroup$ Dec 20 '20 at 8:46
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Checkmate after a pawn captures the moved knight. enter image description here

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  • $\begingroup$ Yes! This is the exact solution I had! Interestingly, all moves here are forced, so black doesn't even need to think about this one. I would be interested to find out whether it's the only solution - that would be surprising. Of course, the pieces on a1 and b1 can be swapped without effect, and in any solution the whole board can be flipped... But apart from that, I don't really know! Maybe I'll have a go at proving it later. $\endgroup$ Dec 20 '20 at 10:20
  • $\begingroup$ Also interesting is that if you have the Queen on a3 it's still checkmate - but in one extra move. $\endgroup$ Dec 20 '20 at 10:23
  • $\begingroup$ You can also swap a3 and c3, and then also move d2 to g4 or h4. But I do not see a truly different mate in one $\endgroup$
    – Retudin
    Dec 20 '20 at 13:51
  • $\begingroup$ In fact, you can't do either of those things because it lets the king escape, preventing checkmate entirely. You can test it on the analysis board to see what I mean. $\endgroup$ Dec 20 '20 at 14:23
  • $\begingroup$ oeps, you are right $\endgroup$
    – Retudin
    Dec 20 '20 at 18:52

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