Answers.Body: <p>You could force a checkmate with two knights and a "king". Because the "king" does not fear being taken, it can move directly in front of the opponent's king, if it is protected by a knight.  All it has to do is do this when the opponent's king is on the side of the board and thus cannot retreat - and it is known that two knights and a normal king can force the opponent's king to the side of the board.</p>
  
  <p>Based on trying it out, I believe a "king" and single knight could also force checkmate. The knight supports the "king" very well, cutting off squares and proving good places for the "king" to advance. And when the knight retreats, the "king" is usually ready to go into that same square if necessary, cutting off the king and forcing it backwards.</p>
  
  <p>With a bishop and a "king", I think the question is whether the king can be forced into a corner which is the same color as the bishop. The following position, with either side to move, results in a quick checkmate, because Black must go into the corner:</p>
  
  <pre><code>[FEN "1k6/8/1K2B3/8/8/8/8/8 b - - 0 1"]
  </code></pre>
  
  <p>I believe this can't be done from many positions, though.  From most positions, the king escapes into the wrong corner. Although it can be driven from that corner, it can then flee to the wrong corner on the opposite side of the board.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-03-07T08:22:43.723Z
Answers.Text: Interesting. It seems the restriction about not moving into check hobbles the king more than I thought as an attacking piece--even a rook can't force checkmate with just a knight. I wonder what other drawn endgames become a win if the attacking side's king is replaced with a "king".
Answers.UserDisplayName: eyeballfrog
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-03-07T12:21:04.107Z
Answers.Text: @eyeballfrog Most pawn and king endgames become a win. Imagine a White pawn on e6 and king on d6. With a normal king, the only way Black can defend is to move his king to d8, to prevent the enemy king from advancing - but in this variation, that allows "K"d7#. With rook and pawn vs rook, Black's defense ordinarily involves as one component giving lots of checks - but now White can ignore the checks, sacrifice his "king", promote the pawn, and go into a queen and rook vs king and rook endgame, which is probably winning (although White does have to be careful not to exchange rooks).
Answers.UserDisplayName: D M
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Answers.CreationDate: 2019-03-07T04:33:37.403Z
Answers.LastActivityDate: 2019-03-07T04:33:37.403Z
Answers.UserDisplayName: D M
Body: <p>Similar to a <a href="https://chess.stackexchange.com/questions/16504/could-two-kings-force-checkmate-against-a-lone-king">previous question</a> of mine, let's suppose there's a piece that moves like the king, but isn't restricted from moving into check.</p>
  
  <p>While a normal king and two knights can't force checkmate, can this "king" and two knights force it by themselves? What about a "king" and a single knight or bishop?</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-03-06T20:52:19.783Z
Comments.Text: Well, what happens if say the black king is on the rim on say e8, and the white king can move into check and is on e7? Is that checkmate, or is black allowed to play Kxe7?
Comments.UserDisplayName: RemcoGerlich
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-03-06T21:20:30.987Z
Comments.Text: @RemcoGerlich Kxe7 is allowed, of course. This piece is not a king--just a piece that moves like one. I don't get why this is so hard for people. And for the close voters--chess variants including nonstandard chess pieces are on-topic. Even *shogi* is on topic and it's far more different from standard chess than I'm proposing here.
Comments.UserDisplayName: eyeballfrog
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-03-06T21:24:56.027Z
Comments.Text: Then you should say so. You call it a king, your piece isn't a king, it's usually known as a Man or a Commoner.
Comments.UserDisplayName: RemcoGerlich
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-03-07T01:59:02.577Z
Comments.Text: I'll call it pseudoking. Do you have the pseudoking AND the normal king or only the pseudoking? If the second case, what are the rules for you getting checkmated?
Comments.UserDisplayName: Pedro A
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-03-07T04:46:50.273Z
Comments.Text: @PedroA You presumably have a normal king somewhere, but the question is whether these pieces can checkmate without his help.
Comments.UserDisplayName: eyeballfrog
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-03-07T06:33:56.437Z
Comments.Text: @RewanDemontay: but then he has to explain how it differs from a normal king. He said it can move into check. OK, but there is also a rule that says the king cannot be captured, and he didn't say that changed as well. Hence the request for clarification. Using the proper name is just an easier shortcut. Also, what was discussed on the other question is irrelevant for this one.
Comments.UserDisplayName: RemcoGerlich
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-03-07T08:17:17.837Z
Comments.Text: Just for information, "non-royal king" is the common term in the world of problems. It's not really necessary to use a completely different name like "Man" for something that quacks like a king. Calling it a "king" with quotation marks seems clear enough. Also, this should not be off-topic, since fairy chess is perfectly fine to be discussed here.
Comments.UserDisplayName: Remellion
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-03-07T10:24:14.157Z
Comments.Text: Such a non-royal king is sometimes named an "erlking" in fairy chess, e.g. in the software Popeye. As a side note since it is not asked in the OP, two erlking will mate a king quite easily, and even the pair king+erlking will succeed.
Comments.UserDisplayName: Evargalo
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-05-15T12:16:52.527Z
Comments.Text: I would call this piece a princess, because it moves like a queen with very short legs. (We are talking toddler princess here.) Contrast with the king, which also moves in all directions but is merely lazy.
Comments.UserDisplayName: itub
Tags: <endgame><checkmate><chess-variants><unorthodox-pieces>
Title: Would certain checkmates be possible if the king could move into check?
ThreadText: # Would certain checkmates be possible if the king could move into check?
  
  (Asked by: username_0 on 2019-03-06)
  
  Similar to a [previous question](https://chess.stackexchange.com/questions/16504/could-two-kings-force-checkmate-against-a-lone-king) of mine, let's suppose there's a piece that moves like the king, but isn't restricted from moving into check.
  
  While a normal king and two knights can't force checkmate, can this "king" and two knights force it by themselves? What about a "king" and a single knight or bishop?
  
  **Tags:** endgame, checkmate, chess-variants, unorthodox-pieces
  
  > **Comments:**
  > **username_1**: Well, what happens if say the black king is on the rim on say e8, and the white king can move into check and is on e7? Is that checkmate, or is black allowed to play Kxe7?  
  > **username_0**: @username_1 Kxe7 is allowed, of course. This piece is not a king--just a piece that moves like one. I don't get why this is so hard for people. And for the close voters--chess variants including nonstandard chess pieces are on-topic. Even *shogi* is on topic and it's far more different from standard chess than I'm proposing here.  
  > **username_1**: Then you should say so. You call it a king, your piece isn't a king, it's usually known as a Man or a Commoner.  
  > **username_2**: I'll call it pseudoking. Do you have the pseudoking AND the normal king or only the pseudoking? If the second case, what are the rules for you getting checkmated?  
  > **username_0**: @PedroA You presumably have a normal king somewhere, but the question is whether these pieces can checkmate without his help.  
  > **username_1**: @RewanDemontay: but then he has to explain how it differs from a normal king. He said it can move into check. OK, but there is also a rule that says the king cannot be captured, and he didn't say that changed as well. Hence the request for clarification. Using the proper name is just an easier shortcut. Also, what was discussed on the other question is irrelevant for this one.  
  > **username_3**: Just for information, "non-royal king" is the common term in the world of problems. It's not really necessary to use a completely different name like "Man" for something that quacks like a king. Calling it a "king" with quotation marks seems clear enough. Also, this should not be off-topic, since fairy chess is perfectly fine to be discussed here.  
  > **username_4**: Such a non-royal king is sometimes named an "erlking" in fairy chess, e.g. in the software Popeye. As a side note since it is not asked in the OP, two erlking will mate a king quite easily, and even the pair king+erlking will succeed.  
  > **username_5**: I would call this piece a princess, because it moves like a queen with very short legs. (We are talking toddler princess here.) Contrast with the king, which also moves in all directions but is merely lazy.  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_6 on 2019-03-07. Score: 5 | Accepted answer
  
  You could force a checkmate with two knights and a "king". Because the "king" does not fear being taken, it can move directly in front of the opponent's king, if it is protected by a knight.  All it has to do is do this when the opponent's king is on the side of the board and thus cannot retreat - and it is known that two knights and a normal king can force the opponent's king to the side of the board.
  Based on trying it out, I believe a "king" and single knight could also force checkmate. The knight supports the "king" very well, cutting off squares and proving good places for the "king" to advance. And when the knight retreats, the "king" is usually ready to go into that same square if necessary, cutting off the king and forcing it backwards.
  With a bishop and a "king", I think the question is whether the king can be forced into a corner which is the same color as the bishop. The following position, with either side to move, results in a quick checkmate, because Black must go into the corner:
  [FEN "1k6/8/1K2B3/8/8/8/8/8 b - - 0 1"]
  
  I believe this can't be done from many positions, though.  From most positions, the king escapes into the wrong corner. Although it can be driven from that corner, it can then flee to the wrong corner on the opposite side of the board.
  
  > **Comments:**
  > **username_0**: Interesting. It seems the restriction about not moving into check hobbles the king more than I thought as an attacking piece--even a rook can't force checkmate with just a knight. I wonder what other drawn endgames become a win if the attacking side's king is replaced with a "king".  
  > **username_6**: @username_0 Most pawn and king endgames become a win. Imagine a White pawn on e6 and king on d6. With a normal king, the only way Black can defend is to move his king to d8, to prevent the enemy king from advancing - but in this variation, that allows "K"d7#. With rook and pawn vs rook, Black's defense ordinarily involves as one component giving lots of checks - but now White can ignore the checks, sacrifice his "king", promote the pawn, and go into a queen and rook vs king and rook endgame, which is probably winning (although White does have to be careful not to exchange rooks).  
  
  ---
  
  