Decimaka (revised)

Decimaka is a western Chess variant that tries to emulate the promotion dynamics of the historic Japenese Chess game 'Maka Dai Dai Shogi';. In particular, promotion is not reserved for Pawns. Most piece types from the initial setup can promote, and the right to promote originates from making a capture, rather than reaching a promotion zone. So promotion can happen everywhere on the board.

This makes tactics highly non-trivial. It also impacts strategy with respect to Pawns.

The original version of this game was published in 2018. Since then it has become clear (also through experience with the smaller variant Veteran Chess, which uses similar promotion rules) that this original design has some flaws. For one, trading of Pawns protected by Pawns was strongly discouraged by the fact that this would result in a promotion on the recapture. This made it very difficult to break down Pawn chains that typically form in western chess variants, and thus made the game very static. In Shogi variants this problem does not exist, as Shogi Pawns can never protect each other. In addition, too many games would end without a Queen ever appearing, because the Fiancees were traded out of the game before they could promote. I also regretted having the Lion demote; in the large Shogi variants the Lion does have a strong promotion, and Decimaka had already many other demoting pieces. Finally I felt there were too many leapers (often leaping in the same way), and too few sliders. The rule changes I made to address these problems are highlighted in boldface below.

Setup

Pieces

• Pawn - moves like orthodox Pawn, including a double push from its initial location, and e.p. capture. Promotes to Omni.
• Tee - steps one square straight forward or backward, or diagonally forward. Promotes to Trident.
• Cross - steps one or jumps two squares in all orthogonal directions. Promotes to Omni.
• Y - slides forward diagonally or backwards along a file, both maximally 3 squares. Promotes to Omni.
• Fiancee - moves like orthodox King (but is not royal). Promotes to Queen.
• Knight - moves like orthodox Knight. Promotes to Nightrider.
• Bishop - moves like orthodox Bishop.
• Rook - moves like orthodox Rook.
• Star - Jumps one, two or three squares orthogonally or diagonally. Promotes to Omni.
• Lion - Moves as King, Knight or jumps 2 squares orthogonally or diagonally. Promotes to Berserker.
• Omni (promoted Pawn, Cross, Y, or Star) - captures one step diagonally, moves without capturing one step orthogonally.
• Trident (promoted Tee) - slides along files, or diagonally forward.
• Nightrider (promoted Knight) - makes arbitrarily many Knight moves in the same direction, until blocked.
• Queen (promoted Fiancee) - moves as orthodox Queen.
• Berserker (promoted Lion)- Moves like a Lion, or slides up to three squares orthogonally or diagonally.
• King - moves as orthodox King. Takes 3 steps towards Rook on castling.

Rules

The game is won by checkmating the opponent King. Stalemate is a draw.

Pieces can (and sometimes must) promote when they make a capture. This can happen anywhere on the board, there isn't any special promotion zone. Promotion is mandatory when you capture a promoted piece; otherwise it is optional, and you can choose not to promote. There never is any choice in what you promote to.

Pawns cannot promote by capturing other Pawns, though.

A piece other than King which captures a Queen or a Fiancee promotes to Queen in the same turn. That also applies to pieces that are already promoted, or would normally not promote at all.

Pawns that reach the final rank are stuck there like dead wood.

Notes

There are four classes of pieces, depending on how they promote:

• Unpromotable pieces (King, Rook, Bishop).
• Pieces that turn from steppers/leapers into the corresponding sliders/riders (Fiancee, Knight, Tee).
• Pieces that promote to Omni (Star, Y, Cross, Pawn). Which, for all but the latter, is actually a demotion.
• The Lion is in a class of its own, and promotes to the even stronger Berserker.

Promotability has a huge effect on tactics. Where without it an exchange typically is most profitable whan you capture with the least-valuable piece first, with it you would try to end with the piece that has the best promotion. Furthermore, when you won't make the last capture yourself, you can sometimes try to discourage the opponent's recapture by promoting (if he can only recapture with a strongly demoting piece). Which is a reason to order unpromotable pieces earlier, even when they are more valuable.

Pawns play a different role as in other chess variants. Creating passers by clearing away enemy Pawns is pointless if there is no promotion zone, and it can be advantageous to preserve enemy Pawns as easy target for promoting your pieces on, even when you could safely capture them with a non-promoting, demoting or already promoted piece.

Last revised by H. G. Muller.