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You have been imprisoned by your super duper cliché evil king named Tim Goldsteen for sneezing during his birthday party. Apparently he’s that evil. Anyhow, you found out Tim’s secret that he enjoys chess and is a grandmaster. However you did that in jail. Not wanting his secret revealed, as the Chess Players Against Evil Grandmasters Society (WHY does that exist? I’m gonna kill whoever wrote this script for me!) was after him, Mr. Goldsteen came up with an idea.

Instead of reasonably stabbing you in the face or something right then and there, he offers to spare your life if you keep his secret. But first you must complete a challenge.

He tasks you with creating a game with the following conditions:

  1. It is white to move and checkmate
  2. Black must have 10 knights in the starting position. Your starting position is to be constructed by you.
  3. All of black’s moves must be knight moves. The black king cannot move at all, i.e. because it cannot, ever.
  4. All of black’s moves are forced, but variations are allowed to occur.
  5. At least 9 of the black knights must move. (I say this because this is the limit that I ran into. I congratulate you if you can get all ten!)
  6. The black king can be the only black piece left at the end of the game.
  7. It must be legal.
  8. FIDE laws of chess apply.
  9. Assume that black is playing optimally.
  10. I may or may not already have a solution.

You have 24 hours to complete the task before he comes back and stabs you in the face or something like he should have done earlier. He manically laughts as he slowly walks off to eat his dinner of turkey fries.

“Call it a not so knights challenge!” Tim Goldsteen yelled before he vanished from your range of hearing.

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    $\begingroup$ "All of black’s moves are forced, but variations are allowed occur." Consequently, I presume that you are asking us to create a position, rather than a game? I mean, there aren't really any forced moves after any white move 1. $\endgroup$
    – Brandon_J
    Commented Apr 21, 2019 at 0:35
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    $\begingroup$ Not bad. Not bad at all. $\endgroup$
    – Brandon_J
    Commented Apr 21, 2019 at 0:42

2 Answers 2

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UPDATE: now a legal solution. Here is a variation; there are many as Black has a lot of possible choices at some point, however what moves Black makes doesn't really matter. This variation is one of the most challenging and it shows all the ideas. If you think you have a refutation I'll be happy to explain. I'll upload more variations later.

Apronus link

[FEN "k1n5/1RQnnQ2/nQnQQ3/1nQ1n3/1n1n4/4Q2B/Q7/K1Q1R2n w - -"]

PGN 1. Rb8+ Ndxb8 2. Qcxb8+ Nxb8 3. Qg2+ N7c6 4. Qcxc6+ Ndxc6 5. Qdxc6+ Nexc6 6. Qcxc6+ N8xc6 7. Qexc6+ Nxc6 8. Qba7+ Nbxa7 9. Qfxa7+ Nxa7 10. Qb6 Ng3 11. Qxg3 Nd8 12. Qf3+ Nac6 13. Qfxc6+ Nxc6 14. Re8+ Ncb8 15. Rxb8+ Nxb8 16. Bg2+ Nc6 17. Bxc6#

A couple of other variations:

[Variant "From Position"] [FEN "k1n5/1RQnnQ2/nQnQQ3/1nQ1n3/1n1n4/4Q2B/Q7/K1Q1R2n w - -"]

  1. Rb8+ Ndxb8 2. Qcxb8+ Nxb8 3. Qg2+ Nef3 4. Qexf3+ Nxf3
  2. Qfxf3+ Nbd5 6. Qfxd5+ Nec6 7. Qcxc6+ Nxc6 8. Qdb8+ Nxb8
  3. Qga2+ Na6 10. Qaxa6+ Nca7 11. Qaxa7+ Nxa7 12. Qdxc6+ Nxc6
  4. Qe8+ Nb8 14. Bf1 Ng3 15. Bg2+ Ne4 16. Qxe4+ Nc6
  5. Qexc6#

[Variant "From Position"] [FEN "k1n5/1RQnnQ2/nQnQQ3/1nQ1n3/1n1n4/4Q2B/Q7/K1Q1R2n w - -"]

  1. Rb8+ Ndxb8 2. Qcxb8+ Nxb8 3. Qg2+ N8c6 4. Qcxc6+ Ndxc6
  2. Qcxc6+ N5xc6 6. Qdxc6+ Nexc6 7. Qexc6+ Nxc6 8. Qfa7+ Ncxa7
  3. Qe8+ Nc8 10. Qxc8+ Nb8 11. Qcxc6+ Nxc6 12. Qa2+ Nba7
  4. Qaxa7+ Nxa7 14. Re8+ Nc8 15. Bf1 Nf2 16. Bg2+ Ne4
  5. Rxe4 Ne7 18. Rxe7#

Note: my first answer below isn't quite a solution since the original position is illegal, as pointed out by the OP in the comments.

Here is a solution where the 10 knights move.

There is a little freedom at each move but not so much, so that it is very easy to check that it works regardless of which variation occurs.

FEN (starting position): nn1nQ3/nQ1Qn3/QR1RRRRR/n1kNn3/Qn1n4/2B5/n1N3B1/7K w - - 0 1

PGN: 1. Rbc6+ Na7xc6 2. Qdxc6+ Nb8xc6 3. Rxc6+ N8xc6 4. Qexc6+ N7xc6 5. Rxc6+ Nexc6 6. Rxc6+ Ndxc6 7. Rxc6+ Naxc6 8. Rxc6+ Nxc6 9. Bb4+ Naxb4 10. Qaxb4+ Nxb4 11. Ndxb4 Nc7 12. Qxc7# *

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  • $\begingroup$ @RewanDemontay Sure: first, promote all the pawns, then bring the kings where they need to be, then put the Black knights on the edge of the board, then all the White pieces, then the four remaining knights, and done. $\endgroup$
    – Arnaud Mortier
    Commented Jun 29, 2019 at 11:14
  • $\begingroup$ @RewanDemontay Right, only six pieces are missing, there would need to be 8. I guess the problem is still open then, good catch. $\endgroup$
    – Arnaud Mortier
    Commented Jun 29, 2019 at 12:52
  • $\begingroup$ @RewanDemontay Updated, with a cleaner initial position (there are less variations to consider). $\endgroup$
    – Arnaud Mortier
    Commented Jul 3, 2019 at 22:50
  • $\begingroup$ @RewanDemontay Thanks. I've added a couple of variations. $\endgroup$
    – Arnaud Mortier
    Commented Jul 4, 2019 at 20:46
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Now that a solution exists with ten knights as I hoped, I shall share the nine I had before asking.

enter image description here 1R1Qn1nR/3n1k1n/1n3n1Q/3nQKQn/3Qn1nQ/2Q5/1Q6/Q7

  1. Qexf6+ Ne4xf6 2. Q4xf6+ Nd5xf6 3. Qcxf6+ N4xf6 4. Qbxf6+ N5xf6 5. Qaxf6+ Nhxf6 6. Qgxf6+ Ngxf6 7. Q4xf6+ Nexf6 8. Qhxf6+ Nxf6 9. Rb7+ Nbd7 10. Rxd7+ Nxd7 11. Qxd7#

Link to game (Apronus)

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