Is there any position where not promoting (illegally) would be the best move?

Question

Is there any position, where moving a pawn to last rank but not promoting it to any piece would be the best move?

By the way, I know this is an illegal move. Assume it is legal.

Edit: Now we have a nice answer from Dag Oskar which ends with stalemate. That's good. But I wonder, if there is winning position, winning by not promoting, and the only winning move is not promoting.

Edit #2: I think a winning position is impossible, as this seems to be occurable when opponent stalemates with promotion. If opponent is not stalemating, then there is no point of not promoting anyway. But if opponent stalemates with a knight, then bishop or rook doesn't stalemate, and etc. It's impossible to have a position where knight, bishop and rook stalemates. So, in every such position, there will be a correct promotion. Not promoting won't be the best move anyway.

Therefore, I'm accepting the answer.

Edit #3: Rosie F's answer demonstrates that it's possible to win with a 'not promoting move'. It's very entertaining to see it's possible.

Answer 1

The Matt Bengtson problem Prof. Elkies mentions is:

[Title "Matt Bengtson, Chess Braintwisters (Burt Hochberg), no. 103. White to move & draw."]
[FEN "4kn2/3p1pPp/4pPpK/6P1/8/2p5/1b6/8 w - - 0 1"]

The start of the solution-line can't be shown in PGN as White's 1st move is illegal: 1. g8=Black queen Qg7+ (anything else stalemates White) 2. fxg7 c2 3. g8=Q c1=Q 4. Qxf7+ Kd8 5. Qe8+ Kc7 6. Qc8+ Kb6 (Kd6 7. Qc5+) 7. Qc6+ Ka7/Ka5 8. Qb7/Qb5, drawing. White's queen is then taken for stalemate. Solution line taken from Chess Braintwisters.

However, the problem is actually cooked with a win for Black starting with “3... f6!”, and there is no stalemate for White. The solution and the cooking line can be played over on the Schwalbe Problem Database.

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(This is in answer to a comment by Prof. Elkies to Dag Oskar Madsen's answer, but, it seems, the syntax that activates the PGN-viewer in answers doesn't do so in comments.)

A similar oddity from the same book:

[Title "John Beasley, EBUR, 1996. White to move & win."]
[fen "5r1K/2k1P3/3N1Bqp/N2Q1B1P/8/8/8/1R6 w - - 0 0"]

This problem was reprinted as no. 107 in Burt Hochberg's Chess Braintwisters.

White is in check, and his only reasonable move is to capture on f8 (1. Qg8? Qxg8#). But 1. exf8=R allows stalemate after 1. ... Qg7+ because the new rook guards d8 after 2. Bxg7. Similarly, 1. exf8=N guards d7 allowing 1. ... Qh7+ and stalemate, and 1. exf8=Q/B guards d6 allowing 1. ... Qg8+ and stalemate. The answer is 1. exf8! (no promotion). Now 1. ... Qg7+ 2. Bxg7 releases d8; 1. ... Qh7+ 2. Bxh7 releases d7; 1. ... Qg8 2. Qxg8 releases d6. 1. ... Qxf6+ destroys the stalemate at once, and White wins. Solution line and discussion taken from Chess Braintwisters.

The is also viewable on the same site as the other problem.

Answer 2

Here is an example:

[fen "8/4P3/8/4p1p1/2p3Pp/p4p1K/k1p2P1P/8 w - - 0 1"]

1. e8 leads to stalemate next move, while all legal promotions lose to 1... c1=Q followed by 2... Qf1#.

Answer 3

Here's another problem where White to move loses, but moving a pawn to the 8th rank and not promoting would (if it were legal) draw.

"By the 19th century [...] it was thought that promotion should give the maximum possible advantage. It was claimed that in some cases the best move would be to remain a pawn, and Kling composed a position to show this:

[Title "Josef Kling"]
[fen "r7/1Pp5/2P3p1/8/6pb/4p1kB/4P1p1/6K1 w - - 0 0"]

If 1 bxa8=any piece, 1 ... gxh3 2 any h2#, but if the pawn on a8 remains a pawn then 1 ... gxh3 is stalemate." - David Hooper & Kenneth Whyld, The Oxford Companion to Chess, 1st ed. (1987) pub. OUP, s.v. promotion (slightly adapted). Dag Oskar Madsen's problem has the same tempo (not sure of the correct term here) as Kling's: White's only mobile unit is the pawn; promotion to any piece enables Black to #2, whereas by making the pawn immobile White immediately stalemates himself.

If Black does not take White’s bishop. then White will play 2. Bxg2 and achieve a fortress position, thereby drawing the game.

Answer 4

In a sense, promoting illegally counts as not promoting. If it isn’t legal under chess law, it officially never happens at all. There are many types of such promotion. I shall give examples of almost all of them. There are no queen problems because there are no known correct problems where White draws by promoting to a Black queen, much less winning by doing so.

Types Of Illegal Promotion

1. King
2. Pawn
3. Pawn, But Promoting Later
4. Enemy king
5. Enemy pawn
6. Enemy knight
7. Enemy bishop
8. Enemy rook
9. Enemy queen

All of the source links direct to pages in the Die Schwalbe Chess Problem Database.

King

[Title "M. Frisbee & Palmer Gunkel Keeney, Pittsburgh Gazette Times 1914, Mate In 2"]
[FEN "5R2/3P4/4k3/8/3K4/8/8/8 w - - 0 1"]

Solution:

1. d8=WK Kd6 2. Rf6#

Source

Enemy King

[Title "Karl Arthur Leonid Kubbel, 1941, Mate In 2"]
[FEN "8/4P1Q1/2P5/8/8/6Pk/5P2/7K w - - 0 1"]

Solution:

1. e8=BK Kd8 2. Qd7##

Source

Additionally, here is another joke problem has castling on the enemy rank.

[Title "Andrew Buchanan After Anonymous, PDB Website 1/15/2019, Mate In 3 Without Queening A Pawn"]
[FEN "2k5/P3P3/P4P2/3P4/3B4/8/8/8 w - - 0 1"]

Solution:

1. e8=K Kc7 2. a8=R Kd6 3. 0-0-0#

Source

Pawn

[Title "Samuel Loyd, American Chess Magazine 12/1898, Mate In 3"]
[FEN "N1Br4/2Pb1P2/3k4/1P2R3/1P2K3/B7/8/8 w - - 0 1"]

1. cxd8! Bf5+ 2. Rxf5 Ke7 3. f8=Q#
(1. cxd8=Q/R? stalemate!)
(1. cxd8=B? Bf5+ 2.  Rxf5 stalemate) 
(1. cxd8=B? Bf5+ 2. Kd4? Bxc8!)  
(1. cxd8=N? Bc6+ 2. bxc6 stalemate!)
(1. cxd8=N? Bc6+ 2. Kd4? Bxa8!)

Source

Even more amazingly, here is a problem in which the best move for both sides is promotion into a pawn.

[Title "Peter Wong & Geir Sune Tallaksen Østmoe, Matplus.net Forum 11/12/17, Black Moves And White Wins"]
[FEN "5qnk/3pPB2/1p1p1N2/1pbK1NP1/1p1pP3/1P1P4/6p1/7R b - - 0 1"]
[startflipped ""]

1. gxh1! exf8! {White easily wins with an extra piece}

Source

Lastly, here is a classic by Thomas R. Dawson in which white promotes to a pawn three times!

[Title "Thomas R. Dawson, The Chess Amateur 1913, White Draws"]
[FEN "6K1/6PP/3p2PP/3P1ppp/8/ppp5/qrp5/1rk5 w - - 0 1"]

1. Kh8 Kd2 2. g8 Re1 3. g7 Re6 4. dxe6 Rb1 5. e7 b2 6. e8 Qxg8+ 7. hxg8 null 8. h7 null {Stalemate}

Source

Pawn, But Promoting Later

[Title "Ado Kraemer, Deutsche Schachblätter 1949, Mate In 3"]
[FEN "7K/5P2/6pp/6pk/6pr/6pb/8/8 w - - 0 1"]

Solution:

1. f8 Bf1 2. f8=Q and Kh7 ~ 3. Qxh7# or 1... g2 2. f8=N & Sd7/h7 ... 3. Nf6#

Source

Enemy Pawn

[Title "James Malcom, PDB Website 3/4/2020, Mate In 2"]
[FEN "1k1K3r/3Q2P1/1N6/8/8/8/8/8 w - - 0 1"]

Solution:

1. gxh8=BP h7,h6 (Pawns are allowed to do a double step on their first move) 2. Qc7#

Source

Enemy Knight

[FEN "8/5RPk/6N1/6K1/8/8/8/8 w - - 0 1"]

Solution:

1. g8=BN#

Enemy Bishop

[Title "James Malcom After Thomas R. Dawson, PDB Website 3/5/2020, Mate In 2"]
[FEN "6B1/2Q2P2/k7/8/K7/8/8/8 w - - 0 1"]

Solution:

1. f8=BB B~ 2. Bc4#

Source

Enemy Rook

[Title "Noam D. Elkies, Outrageous Chess Problems 2005, Mate In 2"]
[FEN "5brk/5Pp1/6K1/6N1/8/8/8/8 w - - 0 1"]

Solution:

1. fxg8=BR B~ 2. Nf7#

Source: