gwalla | Entries tagged with chess variants

Been working on another chess variant. It's a "large board" (10x10) type, and to some extent a kitchen sink variant incorporating a bunch of pieces I find interesting. Still, even though it's not really finished yet, I think it holds some promise.

Each side starts with ten pawns on the third rank, "elemental" pieces on the second rank, and "complex" pieces on the first rank. The elemental pieces are the Rook, Knight, Bishop, and Squire. The complex pieces are the Lionheart King, Queen, Archbishop, Marshall, Cavalry, Gryphon, Hippogriff, and Unicorn.

The Rook, Bishop, and Queen move as they do in standard chess. The Knight is enhanced: It moves as a standard chess knight but, if the square it jumps to is unoccupied, it has the option of sliding one more space diagonally away from its starting rank and file. This sliding move may be used to capture. The Squire (S) moves like a standard chess King, but is not royal: it is not prohibited from moving onto a threatened square, and can be captured like any other piece.

The complex pieces consist of each compound of two elemental pieces, and a "bent" or extended form of each elemental move. The compounds are the Queen (Rook + Bishop, of course), Archbishop (bishop + knight), Marshall (Rook + Knight), and Cavalry (Knight + Squire).

The Gryphon is taken from Grande Acedrex, a very old variant of medieval chess (Shatranj), where it is called a giraffe. Its move is one step diagonally followed by any number of orthogonal steps away from its starting rank or file. It is a "bent rook". The Hippogriff* is its counterpart, starting with a single orthogonal step and proceeding diagonally away from its starting rank and file. It is a "bent bishop".

The Unicorn is a bit odd: it slides any number of spaces, alternating orthogonal and diagonal steps. If another piece is in its path, it may jump that piece like a standard chess knight, but must stop after the jump. This is the extended version of the knight-move.

The Lionheart King takes the place of the bent or extended Squire, and is the royal piece that must be checkmated to win. It takes its name from the lion from Chu Shogi and Dai Shogi**. It moves as a standard chess king, but as a half action, and a player may make one or two half actions in a single turn. It is thus able to capture two pieces in a turn, or capture and move back to its starting square (the latter called igui), though there are restrictions. It cannot end its turn on a threatened square (same as standard chess), it cannot capture on or move through a threatened square to capture unless it captures the only piece threatening that square ("check en passant"), it cannot take its second step if it captures a pawn on the first step ("pawn stalling") and if it starts its move in check it may only take one step unless the second step would capture the only piece giving check ("staring down"). There is no castling; the king is much more mobile in this variant, so there seems to be less need (also, the king and rooks start on different ranks).

Pawns have the same basic move as in standard chess: moving passively one step directly forward, and capturing one step on either forward diagonal. There are a few differences, however. When sitting on the third rank, it can also move passively one step diagonally forwards, but loses this ability as soon as it has left that rank. A pawn move is a half-action, like the Lionheart King's move, but a single pawn cannot be moved twice on a single turn (in other words, you can move two pawns per turn). The only exception is if the pawn has not moved on a previous turn: in that case, it may make two passive moves. A pawn that has made a double move as its first move may be captured by an enemy pawn on the opponent's following turn as if it had only made the first of its two moves (en passant capture). No more than one pawn may capture on a single turn.

To balance first move advantage, white's first pawn move is a full action.

Pawns may promote when they reach the 9th or 10th rank. A pawn may only promote to a piece that has been previously captured by the opponent. Promoting a pawn is a half action, with two restrictions: no more than one of each player's pawns may promote in a turn, and a promotion cannot be the only action taken (at least one half action must move a piece). All of the pieces that a pawn may promote to move as a full action, so it's not possible on a single turn to promote a sitting pawn and then take the promoted piece's move.

Half actions may be mixed. For example, in a single turn a player may move two pawns, or move and promote one pawn, or move a pawn and the king (one space), or move the king two spaces, or move the king one space and promote a pawn.

I haven't really decided on a board setup yet. I think I want to keep the king and queen next to each other in the middle. There are 4 2nd-rank piece types and 10 files, so there will be four of one piece on that rank (probably the guards; they're a bit cannon-foddery) and two of each of the others.

*In his article on bent riders on chessvariants.org, Ralph Betza names this piece the "Aanca", but I don't like that name. It's just Spanish for "gryphon". I prefer Hippogriff because it is like a gryphon, but also like a horse (knight): its move includes the Xiangqi horse (mao, a knight that cannot jump), and it always ends up on a square of the color opposite the one it started on. CV.org uses "hippogriff" for a limited form of the Gryphon, but they seem unlikely to coexist in a single game.

**Old, larger variants of shogi. Chu shogi ("middle shogi") was played with 46 pieces per side on a 12x12 board. Dai shogi ("large shogi") used 65 pieces per side on a 15x15 board. Sho shogi ("small shogi") was played on a 9x9 and evolved directly into modern shogi.

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Current Music: Link Wray - Rumble

Got to thinking about chess variants lately. Specifically, spicing up pawn promotions.

In standard chess, technically a pawn that reaches the back row can promote to any first-rank piece other than the king. In practice, it almost always promotes to a queen, and only very very rarely to a knight. There's no point in promoting to rook or bishop, since the queen contains the moves for both. The choice of promotion would be more interesting if the pawn could promote to any compound of simple first-rank pieces: the queen (bishop+rook), archbishop (bishop+knight), or marshall (rook+knight). Possibly other pieces of similar strength as well.

The idea of allowing pawn promotion to fairy chess pieces not found in the starting array is not new. My idea is for the promotion to be undeclared, and revealed by how the piece is moved. There would therefore be an element of deduction on the part of the opposing player. For example, if the promoted pawn slides orthagonally, the player knows that it has a rook component (a queen or marshall); if it later makes a knight's move, it must be a marshall.

A bit like a particle in quantum mechanics, its move only "collapses" into something definite as it is observed. Until the player commits to a specific move, it could be anything. In other words, the player doesn't have to decide on a promotion as soon as the pawn reaches the back row, but fixes components as he goes. If only one component has been used (for example, an orthagonal move meaning the piece is part rook), the player can still keep his options open and decide whether it's also part knight or part bishop later.

We can say that a pawn that has reached the 8th rank but has not moved yet is unexposed: its nature is not known. One that has made only one type of move is partly exposed. One that has made two types of moves is fully exposed: its move possibilities are fixed, and it is effectively

The problem here is that a pawn that is not yet fully exposed is immensely powerful. If it is unexposed, it threatens all of the squares for any of its potential moves (since it's free to choose any of those moves as a component). If partly exposed, it still threatens all squares for all possible components, because it is still indeterminate between the two unknown components. This is way too powerful, effectively an amazon (rook+bishop+knight): the game Maharajah and the Sepoys pits a single royal (kinglike: unable to move into threatened squares, game lost if it cannot escape capture) amazon on one side against an entire chess army on the other, and the full army only barely outclasses it. To fix this, we can rule that squares are only threatened if the player reveals that they are on his turn (explicit), or they are threatened by a move that has already been exposed (implicit). If the space is not threatened (explicitly or implicitly), the promoted pawn is not allowed to capture a piece that moves there on the next turn (although it may fix a component later that would have allowed it to make that capture if it had been set beforehand).

This rule could also be limited to determining threatened squares only for purposes of giving check (since a king is not allowed to move into check).

Let's add another possible promotion to the mix. A piece with the king's move (minus royal restrictions and castling) is called a "mann", and is a valid basic piece that could be used as a component. The combination of a mann and knight is called a centaur, and while it is short-range and seems weak, it is actually a pretty strong piece in the same range as the previously mentioned compounds (and maybe a bit stronger than the bishop+knight). Mann+bishop and mann+rook can be safely ignored; while perfectly valid pieces in their own right, they are both subsets of the queen and therefore redundant in this case.

The addition of this piece causes some interesting complications. A single-space move, orthagonal or diagonal, no longer unambiguously reveals a full component (a knightwise move still reveals a knight component on its own). A piece that has made a knight's move and a single-space orthagonal move may be a marshall or a centaur (if it also makes a single-space diagonal move, though, it's clearly a centaur; if it slides more than one space orthagonally, it's clearly a marshall). A piece that has made a single-space diagonal move and a knightwise move could be archbishop or centaur. One that has moved only like a king may be queen or centaur.

Now another type of piece: the bent riders gryphon and aanca. Technically these aren't compound pieces at all: a gryphon moves one space diagonally followed by sliding at least one orthagonally away from the starting space; the aanca swaps these (one orthagonal, multiple diagonal). However, I believe they around the same range of strength, especially in the endgame when the board is relatively cleared out. They also make deductions more complicated, because they include the knight's move, but not exactly. Unlike a knightwise jump, they can be blocked: a gryphon on a diagonally adjacent square, the aanca on an orthagonally adjacent square. An unimpeded knight's move could be any piece but a queen, but if there was a piece in the way, the possibilities narrow.

While it seems like this element of uncertainty would be a sort of "wild card", the game is still actually deterministic. It may not seem so, but it is still a complete information game: the possible moves of every piece are known to both players.

Another way of achieving a "black box" effect of pawn promotions would be for a player who promotes a pawn to determine at the time of promotion which piece it now is, note it down, and hold to that decision. Under this rule, there would be no "declared threat": if the piece can capture with one of its moves, it can, and if the opposing player moves his king to a threatened square, he must be told that he has moved into check and allowed to take back the move. While this is probably easier to understand, it actually does add an incomplete information aspect to the game, and would play very differently. Call this one "Clue Chess".

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Current Music: The Darkest of the Hillside Thickets - The Innsmouth Look

Been a while since I've messed with chess variants. Here's one based on chess's predecessor, Shatranj (aka medieval chess). It uses a standard 8x8 board, and can be played with a standard set of pieces with a couple of additions (checkers will do in a pinch).

There are 7 kinds of pieces in the starting array:

Pawn - These behave just like Shatranj pawns (i.e. like modern chess pawns without an initial double-step option or en passant).
Knight - The same as modern chess knights (leaping in an L-shape over any intervening pieces). The knight promotes to a warrior.
Fers (councillor) - Steps one square at a time diagonally. In Shatranj, this is the equivalent of the modern queen, but here it replaces the alfil (elephant), which is the equivalent of the modern bishop. The fers promotes to a bishop.
Thief - Leaps two squares diagonally or orthogonally over any intervening pieces. Fairy chess problemists call this piece an "alibaba" (alfil + dabbabah), so I called it a thief. It is colorbound, and can only visit ¼ of the squares on the board. If necessary, it may be represented on the board by a single checker (black for black, red for white). It promotes to an assassin.
Wazir (vizier) - Steps one square at a time orthogonally. Represented in a modern set by the queen. It promotes to a grand vizier.
Rook - The same as the modern rook: sliding any number of squares orthogonally until reaching an obstacle or the edge of the board. It is the one starting piece that does not promote.
King - Same as the modern chess king. Moves one square at a time orthogonally or diagonally. It may not move into a threatened square nor remain under attack at the end of the player's turn (check), and the game is lost when it cannot avoid capture (checkmate). It promotes to a warrior king.

Each player has 8 pawns, one king, one wazir, and two of each other piece. Pawns start on the third rank, rooks in the corners of the first rank, and everything else on the second rank in the order. The thieves are the outermost pieces, followed by the knights, then the fers, with the king and wazir in the middle. The king is on the left and the wazir on the right for white, and vice versa for black: think a stardard chess setup with thieves in place of rooks, fers in place of bishops, and wazir in place of queen.

The following pieces are obtained only through promotion. To mark them, I suggest placing a checker under the basic piece (so a warrior would be a knight on top of a checker, an assassin would be a stack of two checkers, etc.).

Warrior - This piece may move as a knight, or may move one space orthogonally.
Bishop - The same as a modern bishop: sliding any number of squares diagonally until reaching an obstacle or the edge of the board.
Assassin -The thief does not gain a new form of movement by promotion. Instead, it gains a new form of capture, by overtaking: the assassin may capture by jumping over an enemy piece and landing on an unoccupied square. While it is still can only visit ¼ of the squares on the board, it is capable of capturing pieces on all squares with the exception of the player's first rank and the file opposite where the thief started. Note that the assassin may only capture by overtaking if its landing square is empty; it cannot capture two pieces (one by overtaking, one by displacement) in a single move.
Grand Vizier - Moves as a king (one square, any direction), but is not subject to restrictions against moving into or staying in threatened squares, and it may be captured like any other piece. It may additionally promote to a regent by returning to the player's first rank.
Warrior King - May move as a king or as a knight. Rules regarding check and checkmate are still in force.
Regent - Moves as a king or grand vizier. When a player has a regent, he is immune to check and checkmate, and his king (or warrior king) may freely move into or stay in threatened squares. If the king is captured, the regent immediately becomes the new king (thus there is no more regent, and check and checkmate are once again enforced). Note that if a warrior king is captured, the regent still only becomes a plain king, not a warrior king; however, it may promote as a king.

A piece is promoted by landing on the 8th rank (the opponent's home row). Promotion is automatic.

Checkmate is a win. Stalemate is a win. Baring the king (capturing all of an opponent's pieces except for the king) is a win, unless the opponent can bare one's own king in the next move, which is a draw. There is no castling and no en passant. These rules are all the same as in shatranj.

The occasional rule that a king in check may switch places with a friendly piece once in a game is not present (the wazir/grand vizier/regent promotion track serves a similar purpose). The medieval chess rule of the "king's leap" (the ability for a king to make a knight's move once per game) is also not present (the promotion of the king to warrior king gives a more general mechanism for this).

The idea is to get a more dynamic game using primarily short-range pieces (like classic shatranj). The two sides start very close to each other, letting the weaker pieces get into the thick of things more quickly. All of the pieces' movements are either found in shatranj or shatranj variants (like Tamerlane Chess), or are combinations of those moves. For example, the thief combines the 2-square diagonal leap of the traditional shatranj alfil (a very weak piece, only capable of reaching 1/8 of the squares on the board!) with the 2-square orthogonal leap of the dabbabah (war machine), which is found in some old variants. The only exception is the assassin's capture, which has no equivalent in any predecessor or traditional relative of chess (with the possible exception of the chu shogi lion, which is considerably more powerful). The double promotion of the wazir and "substitute king" rule is adapted from the "pawn of pawns" and "pawn of kings" rules of Tamerlane Chess.

The assassin's capture can be quite dangerous: an assassin may capture a piece that is "protected" by another piece without risk of being captured.

I haven't decided how pawns should promote. One option is to let them promote to any other starting piece (other than the king, of course), which can not promote further. Another is to stick with the shatranj promotion rule in this case and only allow them to promote to the queen-equivalent (in this case, the wazir) without being able to promote further. Still another would be to allow promotion to any basic type, with the ability to promote further by reaching the player's 1st rank. I'm undecided.

Another change I'm pondering is adding two more thieves to the initial array (bringing it up to 4 thieves per player), starting on the 1st rank, each a knight's move away from the closest thief on the 2nd rank. This would allow all of a player's thieves, taken together, to visit any square on the board. Since these 1st-rank thieves could never reach the 8th rank, they would have to promote on the 7th. I'm currently leaning towards this.

Current Mood: creative

Got another chess variant for y'all. This one is partly inspired by Alice Chess.

Underworld Chess

This is played with a standard chess army (plus two extra kings) on two 8x8 boards. The regular armies are set up as normal on one board (the World), while the two extra kings are set up on the usual king positions on the second board (the Underworld). The object is the checkmate the opponent's king on the World.

Play is the same as in orthochess, except that when a piece is captured it is dropped on the nearest unoccupied square on its home file in the Underworld (pawns cannot occupy the first rank when dropped, and are dropped on the same file they are captured on). Play on the Underworld is the same as play in orthochess, with the following differences:

Only the enemy Underworld King is capable of actually capturing pieces permanently. Otherwise captures in the Underworld are treated exactly the same as captures in the World, resulting in the piece being dropped back in the Underworld.
There is no pawn promotion. To pawns, the board is cylindrical, with the first rank following the eighth.
Underworld Kings have the same restrictions as regular Kings, except that "checkmating" them does not end the game, and if the Underworld King cannot escape check, its player may make any otherwise legal move. Successfully capturing an Underworld King with a regular piece results in the regular piece being returned to the World in the closest unoccupied space on its home file (the file it captured on for pawns). If the capturing piece is the other Underworld King, the capturing player gets to choose any of his pieces (including "permanently" captured ones) to return to the World, and the captured Underworld King is returned by its player to any unoccupied and unattacked space on his first rank (2nd rank if there are no qualifying spaces in the first).

The full turn order is: white on World, black on World, black on Underworld, white on Underworld. So, while white has the same first-move advantage on the World as he does in orthochess, black has first-move advantage on the Underworld. If either board is reduced to only its native Kings, it is rendered inactive immediately and play there stops until another piece is introduced. White always gets the first move after activation of the World, and black always gets the first move after activation of the Underworld, regardless of who had the last turn before it was deactivated. Deactivating both boards (which can only be done by capturing all non-Kings with Underworld Kings) counts as a draw.

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Current Music: Hideki Naganuma (Jet Grind Radio) - Humming the Bassline

Philosopher Kings

In this chess variant, named after the concept of an "ideal government" from Plato's Republic, the King is a "Philosopher"-like piece. The supplemental 4×4 board is called the Æon, and the King's two kinds of movement are represented by a pair of markers caled Ideas, which move one space at a time orthogonally on the Æon (and cannot share a space). However, unlike in Dialectic Chess, the two Ideas do not correspond to passive and capturing movements: the moves represented by either marker can be used to move passively or to capture. The Ideas start on {1,0} and {1,1}, meaning that the King moves at the start just like a standard chess King. The same restrictions on repeating positions on the Æon between board moves apply as in Dialectic Chess.

Obviously, you couldn't move an Idea if your King is in check, since it could not remove check. It's also impossible to give check by making an æonic move, since doing so would also put your own King in check.

I'm conflicted about castling. Of course, you could play with traditional castling, or with no castling alowed at all. My current idea is that castling is allowed, but only if the King could arrive at the proper spot by repeated use of one of his moves in the same direction (in other words, one marker would have to be on any of {1,0}, {0,1}, {2,0}, or {0,2}). The usual restriction on inability to move the King through a space under attack holds, but if the King would not land there during his moves, the attack is irrelevant: e.g. if space F1 is under attack and one of the markers is on {2,0}, the player could castle kingside as the King would not be considered to have passed through F1 (however, this would leave the rook vulnerable to attack, so it might not be the best move to make in practice). The only real problem with this is that it's kind of hard to describe, but it does make the Æon relevant to castling.

( Royal Philosophers )
( Philosopher's Army )
( Grand Philosopher's Army )
( Chiron's Chess )
( Guru and the Sages )

Possibilities for future exploration

Philosopher-hoppers are possible.

All of these "philosophical" variants of chess use a smaller two-dimensional chessboard to control the "philosophers". It may be possible to expand these concepts. For example, adding a third dimension in which the "thoughts" can move, which could determine another component of the affected piece. Or, staying in 2D, adding a "sub-thought" piece that can split from and merge with a rider's thought that would determine the direction of the first step of a rider's move, allowing a rider to become a bent rider (like a gryphon or unicorn) or a "skip rider" (a similar idea, except the initial move is in the same direction as the rest and only differs in length, like a wazir + dabbabahrider). In fact, there is no reason why the meta-"board" must resemble a chessboard at all!

Current Mood: creative

One of the more intriguing chess variants to be found in The Chess Variants Pages is Philosopher's Chess, a small chess variant (40 spaces total on the board) that introduces an odd new piece: the Philosopher. The interesting thing about the Philosopher is that its movement abilities can change over the course of the game, controlled by another piece (the "Thought") on a separate board (the "Mind"), by both players.

This has inspired me to invent several chess variants with Philosophers and Philosopher-like pieces. Here's one; I'll post the others later:

Dialectic Chess

This variant is played on a standard 8×8 board with an additonal separate 3×3 board. It uses standard chess armies (the knight pieces can be used to represent the Philosophers) plus two differently-colored markers (a pair of checkers pieces would do).

The 3×3 board is the "dialectic", and its ranks and files are numbered 0–2. The two tokens are the "Thesis" and "Antithesis". The position of the Thesis on the dialectic determines how the Philosopher moves passively, and the position of the Antithesis determines how it moves to capture. They start on squares (1,2) and (2,1), respectively (meaning that, at the start, all Philosophers move and capture as Knights). Either player may, on his or her turn, move the Thesis or Antithesis one space orthogonally instead of moving one of his or her own pieces, with the caveat that a dialectic position cannot be repeated between moves on the main board (meaning that you can't simply undo your opponent's dialectic move immediately).

The setup on the main board is identical to that of othochess, but with the Philosophers taking the place of the Knights. Philosophers are leapers (making a single step for a move, ignoring intervening pieces, like a Knight), moving according to the positions of the Thesis and Antithesis: the coordinates are interpreted as a number of spaces in any orthogonal direction followed by a number of spaces at 90° to that, e.g. if the Thesis is at (1,2) or (2,1), the Philosopher moves passively as a Knight, at (1,0) or (0,1) as a Wazir, at (1,1) as a Ferz, and at (0,0) not at all. If a Philosopher captures another Philosopher, it is promoted to a Great Philosopher. Great Philosophers behave like Philosophers, but are riders, taking any number of Philosopher steps in the same direction, rather than leapers. So, with the Thesis at (1,2) or (2,1) a Great Philosopher moves passively as a Knightrider, at (1,0) or (0,1) as a Rook, and at (1,1) as a Bishop.

The usual restrictions on moving into and in check apply to moves on the Dialectic: you cannot move the Antithesis such that it would cause an enemy Philosopher to immediately threaten your King, and if your King is in check you may only make a Dialectic move if that would remove check.

Variant: Hegelian Dialectic Chess — the Thesis and Antithesis may occupy the same square, and if they do they may be moved as a unit, called the Synthesis. This removes an odd side effect of the basic rules, which is that a Philosopher that can move passively on the diagonal cannot capture in the same way that it moves, and vice versa. It also makes a little less than half of the Dialectic pointless, so you could play with all of the Dialectic squares nothwest of the main diagonal removed, giving the Dialectic a stairstep shape.

Current Mood: creative

As I said in an earlier entry, I've recently become interested in chess variants and fairy chess pieces. Well, I've come up with a few of my own. None have been playtested yet, but I hope to eventually register my copy of Zillions Of Games (an interesting "universal" board game engine, complete with network play and an AI that can play any game you implement for it) and implement them.

My current favorite of the variants I've designed so far is Cold Fusion Chess. It's sort of a hybrid of Grand Chess, Fusion Chess, Pocket Knight Chess (and an informal variant idea involving demotions that appeared in the discussion thread on Pocket Knight), and a little bit of Shogi.

Setup:

As in Grand Chess. Additionally, each player has two places to put captured pieces: the Safe Pocket and the Demotion Pocket.

Pieces:

The pieces at the start are the same as in Grand Chess. There are additional pieces, though, which can appear as the result of fusions. The linked article on Fusion Chess lists most of them, but there are a few that are not found in either (although many can be found in other chess variants):

Berolina Pawn — sort of the inverse of a pawn, it can move passively (that is, without capturing) one space diagonally forward, and capture one space straight forward. It is considered a kind of pawn.
Sergeant — a combination of a regular pawn and a berolina pawn, it can move and capture one space in any of the three forward directions. It is capable of capturing en passant. It is also considered a kind of pawn.
Knightrider — can move any number of knight's moves in the same direction until it encounters an obstacle.
Archbishop — moves like a bishop, but may reflect once 90̊° off of the edge of the board.
Chariot — moves like a rook, but may turn once 90° and continue as a rook when it encounters an obstacle (an edge of the board or a friendly piece). As far as I know, this piece is unique to Cold Fusion Chess.
Cavalry, Berolina Cavalry, Cavalry Sergeant — may move as a knight or as a pawn, berolina pawn, or sergeant, respectively. Chess problemists call the Cavalry a Dragon, but Fusion Chess already calls the king + rook combination a Dragon King, and I wanted to avoid confusion.
Templar, Berolina Templar, Temple Sergeant — may move as a bishop or as a pawn, berolina pawn, or sergeant, respectively.
Guard, Berolina Guard, Guard Sergeant — may move as a rook or as a pawn, berolina pawn, or sergeant, respectively.

Rules:

The same as standard chess, with the following changes:

Instead of making a regular move, a player may pocket one of his own men by moving it to his demotion pocket—basically, capturing his own piece. The king may not be pocketed. A player can only do this if he could make a regular move (that is, he's not otherwise stalemated).
Instead of making a regular move, a player may drop a pocketed or captured piece onto an empty square. Captured pieces dropped in this way switch their allegiance to the player who dropped them (as in Shogi). If the piece was dropped from the safe pocket, it remains the same kind of piece. If it was dropped from the demotion pocket, it becomes a different piece of equal or reduced value (see Demotions). Obviously, a player cannot do this if his pockets are empty. A player may not drop when his king is in check, even if it would break check. A pawn cannot be dropped on the 9th or 10th rank.
Pieces captured by regular (non-pawn, non-king) men are put in the capturing player's demotion pocket. Pawns captured in this way are removed from the game. Pieces captured by pawns (or by using the pawn component of a pawn-hybrid piece) or by a king go in the capturing player's safe pocket.
Pawns have the option of promoting on the 9th rank, and must promote on the 10th (this is the same as Grand Chess). Pawns may only promote to friendly non-pawn (note that berolina pawns and sergeants are considered pawns) pieces that the opponent has captured—when this happens, the captured piece is removed from the opponent's pocket and replaces the promoted pawn (without demoting), which is removed from play. A pawn cannot promote if the opponent is not holding any friendly pieces in his pockets, and therefore may not move to the 10th rank at all in such a situation, but may still threaten the opposing king with check from the 9th.
A piece may move onto the same square as a friendly piece and fuse with it. For a pawn to fuse with another piece, the pawn must be the one to move, using its capturing movement. See Fusions.
A compound piece (one formed from two or more other pieces) can split, moving a component piece away from the compound and leaving the other component(s) behind. The moving component moves using its normal movement (e.g. a bishop splitting off from a queen can only move away diagonally, not orthagonally) and cannot capture or fuse on the same turn. A pawn splitting off from a compound onto the 9th or 10th rank promotes as usual (optional on the 9th, mandatory on the 10th); however, a pawn left behind on the 9th by another piece splitting off from a compound does not have the option of promoting, and a pawn cannot be left behind on the 10th rank by a split. Note that the queen, cardinal, and marshal in the starting lineup are considered compounds and can split.

Fusions:

Fusions work similarly to the ones in Fusion Chess, but are a little less restricted. For one thing, pawns can fuse. However, there are still restrictions:

Each piece has a "weight": all non-compound non-pawn men including the king have weights of 1, basic pawns have weights of 1/3, and compounds have weights equal to the sum of the weights of their components. No compound may be formed with a weight exceeding 2.
No more pawns may be added to a sergeant.
The king may not fuse with pawns and vice versa.

Fusions result in the same compounds as they do in Fusion Chess, when applicable. The following are the fusions not found in Fusion Chess:

Pawn + pawn → Berolina pawn
Pawn + berolina pawn → Sergeant
Rook + pawn, berolina pawn, or sergeant → Guard, berolina guard, or guard sergeant respectively
Rook + rook → Chariot
Bishop + pawn, berolina pawn, or sergeant → Templar, berolina templar, or templar sergeant respectively
Bishop + bishop → Archbishop
Knight + pawn, berolina pawn, or sergeant → Cavalry, berolina cavalry, or cavalry sergeant respectively
Knight + knight → Knightrider
Guard, Templar, or Cavalry + pawn → Berolina guard, berolina templar, or berolina cavalry respectively
Guard, Templar, or Cavalry + berolina pawn → Guard sergeant, templar sergeant, or cavalry sergeant respectively
Berolina guard, berolina templar, or berolina cavalry + pawn → Guard sergeant, templar sergeant, or cavalry sergeant respectively

Demotions:

Compounds with pawn components lose one pawn component (as if it had split out) when demoting. All other demotions follow this sequence: Queen → Marshal → Cardinal → Chariot → Archbishop → Knightrider → Rook → Bishop → Knight → Sergeant → Berolina pawn → Pawn. Pawns do not demote.

I think that's everything. Yeah, it's quite a bit more complex than regular ol' chess.

EDIT: clarification of splitting pawns and promotion, minor format fix, "turning rook" now "chariot"

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