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This page is written by the game's inventor, Mike Reeves-McMillan.

Merger Chess

By Mike Reeves-McMillan


The following are the rules for a chess variant. It will be evident that, because all pieces remain on the board at all times, the middle game is greatly changed and the endgame completely changed from conventional chess. Chess is a game of complex strategy; Merger Chess is a game of extremely complex strategy.


  1. Unless otherwise stated, all the normal rules of chess apply in Merger Chess also.
  2. When one piece "captures" another, instead of the captured piece being removed from play it is "merged" with the capturing piece to form a new composite Piece. (To assist explanation, a composite or merged Piece is capitalized, while the individual pieces that make it up are not.)
  3. Anything that is true of a non-composite piece is also true of a composite Piece, but not necessarily vice versa. For example, in rule 2 above the references to "captured piece" and "capturing piece" apply whether the pieces are composite or not.
  4. Ownership and control:
    1. If the composite Piece contains more black pieces than white pieces, it belongs to the black player. If it contains more white pieces, it belongs to the white player.
    2. If it contains an equal number of black pieces and white pieces, it belongs to neither player but may be moved by the player whose pieces are the same colour as the square on which the Piece is currently situated. That is, if the Piece is on a white square it may be moved by the white player, and if on a black square, by the black player.
    3. A Piece consisting of equal numbers of black and white pieces is referred to as a "grey" piece.
  5. A composite Piece may not consist of more than four pieces.
  6. A Piece of four pieces may not move. However:
    1. The player who is entitled to move it (under rule 4) may split it into two Pieces each consisting of two pieces, and move one of them in any legal way while leaving the other in situ.
    2. The piece left in situ may be moved on a subsequent turn.
    3. Alternate rule: the two Pieces formed need not each consist of two pieces; one may consist of three pieces and the other of one.
  7. If a Piece of four pieces is captured:
    1. The capturing player must return to their original starting positions a sufficient number of the captured Piece's component pieces to reduce the total on the square to four.
    2. If the capturing piece is composite, the four pieces left on the square must include all the pieces that make up the capturing Piece.
    3. If the capturing piece is not composite, the capturing piece must be one of those left on the square.
    4. If the returned pieces' original squares are occupied, the returned pieces merge with the pieces which are on the original squares according to all the merge rules, including this one.
    5. If all the rules cannot be followed the capture is not permitted.
  8. A grey Piece of two pieces may move in the manner of either of its component pieces. For example, if it is merged from a knight and a rook it may make a knight's move or a rook's move.
  9. A black or white Piece of three pieces may move in the manner of either of its component pieces of the predominant colour. For example, a piece merged from a black knight, a white rook and a black bishop may make a knight's move or a bishop's move, but not a rook's move.
  10. A black piece may not capture a black piece or a white piece a white piece by a conventional move. However:
    1. Composite Pieces consisting only of one colour may be formed by splitting a composite Piece of four pieces.
    2. A piece being returned to its original square under Rule 8 may merge with a piece of its own colour which is occupying that square.
    3. A composite Piece of only one colour may move in the manner of any of its component pieces.
  11. On reaching the eighth rank, a pawn may be promoted into any other piece. This includes a pawn which is part of a composite Piece. The piece's allowed move changes accordingly.
  12. Check and checkmate do not exist. Rather, the game is won by capturing the opponent's king in such a way that the resulting Piece is either grey (a "grey win") or your own colour. (Capturing your opponent's king in such a way that the resulting Piece is the opponent's colour – i.e. with a grey Piece of two pieces – just gives your opponent a very powerful king.)
  13. Castling is permitted only if neither the king nor the rook involved has moved, or been merged, during the game so far.