Fusion Chess

Fusion Chess is a Chess variant in which pieces may merge together or split apart. In some philosophical inquiries into personal identity, fusion is the process whereby two individuals merge together as a single individual, and fission is the process whereby a single individual divides into two people. Fusion Chess borrows these concepts of fusion and fission from personal identity theory and applies them to Chess pieces. Fusion and Fission Chess would be a more descriptive name, but I favor the shorter name Fusion Chess. Fusion is also one of my favorite forms of music, though that is incidental to the name. Fusion Chess also draws inspiration from Power Rangers and other Sentai shows where the heros merge their ships together into more powerful fighting machines, and it is related to my other game Sentai Chess, which is more closely based on this idea.

2020 Update

Though originally created in 1999, the rules have been updated in 2020. I originally began to update the rules in 2006. This is documented in the Zillions file I was working on. One change made at that time was to transfer the power of initiating royal fusion from the King to the other pieces. This was to prevent the King from using fusion to escape check. The other change was to prevent the King/Rook and King/Bishop compounds from moving through check. This was to keep their greater power from making the game too drawish.

I probably shelved the original changes because of difficulties programming the Zillions file, or maybe I just forgot about it. I got back to it in 2020, when I began working on a Game Courier preset for playing Fusion Chess. I decided to keep the changes from 2006 and make some additional changes. One change is that fission is not allowed for a piece that is attacked. This prevents fission from being used to escape check in positions that would otherwise be checkmate. It does this by preventing a checked royal piece from splitting apart, and by preventing a pinned piece from splitting off a component to block another check. Although it allows an unpinned piece to use fission to block a check, this is allowed only when a player could also block check by moving the whole piece.

One more change is to allow castling. Back when it was up to the King to initiate fusion, it wasn't as important to allow castling. With that power transferred to other pieces, it makes more sense to allow castling. For the purposes of castling, any participation in fission or fusion counts as a move by that piece. So, if a piece moves to the King's space, then moves away without the King changing position, the King is considered to have moved, and it can no longer castle. The same goes for fusion and fission with a Rook. Even if the Rook doesn't change position, it can no longer castle.

Besides changing the rules, I changed some piece names. The Pope is now a Pontiff, and the Eques Rex is now a Cavalier King. Pontiff seems a bit more non-denominational than Pope, and I would rather use English than Latin. The name Cavalier King echoes my use of the same piece in Cavalier Chess, and while being in English, it happens to use the French word for the Knight in the name of the piece that can move as a King or Knight. One more new change is to forbid the Cavalier King from passing through check when it makes a Knight leap. This puts it more on par with the similarly restricted Dragon King and Pontiff.

In May 2020, a discrepency came up between how the game worked in Zillions-of-Games and how it worked in Game Courier. When a royal compound seemed to be attacking a non-royal compound, and it could not capture it without passing through check, Zillions-of-Games would not let the non-royal piece split apart, but Game Courier would. Since I could not figure out how to make Zillions-of-Games behave like Game Courier, but I could get Game Courier to behave like Zillions-of-Games, I went with the interpretation enforced by Zillions-of-Games. This interpretation has the advantage of adding a little more clarity to the game.

Most of these changes are to make the game less drawish. Thanks to the restrictions on fission and on royal fusion, any position that would be checkmate without rules allowing fission and fusion will still count as checkmate. Thanks to not letting royal pieces pass through check, it becomes harder for someone with one of them to easily elude checkmate. In time, these changes will be applied to the games based on Fusion Chess, which include Metamorphin Fusion Chess, Fusion Chessgi, Bedlam, Thunder Chess, Mini Thunder Chess, Fusion Diamond 41, and Assimilation Fusion Chess.

Equipment

A regular 8x8 Chess board, all the regular Chess pieces, and other pieces for Marshalls, Paladins, Pontiffs, Dragon Kings, and Cavalier Kings.

Alternately, the game can be played entirely with regular Chess pieces, with pairs of simple pieces used for compound pieces. Doing it this way will make the combination and division of pieces much easier to handle, and it doesn't require anything but the regular equipment. At startup, replace the Queen with a Rook/Bishop pair. You'll need an extra Chess set for the extra Rook and Bishop.

Setup

The initial setup for Fusion Chess is exactly the same as for regular Chess. So there is no need for a diagram.

Rules

Fusion Chess is played like FIDE Chess with the following exceptions:

• A non-royal simple piece (Knight, Bishop, or Rook) may combine with another simple piece on the same side (including a King) by moving onto its square.
• The combined piece is the piece which moves as either of the two pieces just combined.
• King + Bishop = Pontiff
• King + Rook = Dragon King
• King + Knight = Cavalier King
• Bishop + Rook = Queen
• Bishop + Knight = Paladin
• Rook + Knight = Marshall
• A piece may not combine with another piece of the same type.
• Knight + Knight = Rook + Rook = Bishop + Bishop = Illegal.
• A King may not move to combine with another piece, though another piece may move to combine with its King.
• A piece may combine only with a piece belonging to the same player.
• Compound pieces may not combine with other pieces.
• An unattacked compound piece may split into its components by moving one of its components, under its own powers of movement, to an empty square.
• A Rook which separates from a piece must move away as a Rook moves.
• A Bishop which separates from a piece must move away as a Bishop moves.
• A Knight which separates from a piece must move away as a Knight moves.
• A King which separates from a piece must move away as a King moves.
• The compound piece is replaced by the component which doesn't move away.
• For castling purposes, any piece that has participated in fission or fusion may no longer castle.

• Pawns may promote to Rook, Bishop, or Knight, but not to any compound piece.

• The object is to checkmate your opponent's current royal piece, which may be a King, Pontiff, Dragon King, or Cavalier King.
• No royal piece may move through check when moving more than one space. For the Dragon King and Pontiff, the meaning of this is straightforward. For the Cavalier King, the Knight move is understood as beginning orthogonally and turning diagonally or vice versa. As long as it has an unchecked path to its destination, and the move does not place it in check, its Knight leap is legal. If both spaces it might pass over to reach a space are checked, it cannot move there. However, this does not limit its ability to check or attack a piece.

Pieces

Rook (R)

The Rook moves as the Rook in Chess, any number of spaces orthogonally, going no further than the first occupied space. A Rook may merge with a Knight to form a Marshall, with a Bishop to form a Queen, or with a King to form a Dragon King.

Bishop (B)

The Bishop moves as the Bishop in Chess, any number of spaces diagonally, going no further than the first occupied space. A Bishop may merge with a Knight to form a Paladin, with a Rook to form a Queen, or with a King to form a Pontiff.

Knight (N)

The Knight moves as the Knight in Chess, leaping directly to a space that is one rank and two files or one file and two ranks away. A Knight may merge with a Rook to form a Marshall, with a Bishop to form a Paladin, or with a King to form a Cavalier King.

Queen (RB)

The Queen moves as the Queen in Chess, any number of spaces in any single direction, going no further than the first occupied space. The Queen is a compound of Rook and Bishop. It may separate into its components by moving one of them to an empty space.

Marshall (RN)

The Marshall moves as a Rook or Knight. The Marshall is a compound of Rook and Knight, and it may separate into its components by moving one of them to an empty space.

Paladin (BN)

The Paladin moves as a Bishop or Knight. The Paladin is a compound of Bishop and Knight, and it may separate into its components by moving one of them to an empty space.

King (K)

The King moves one space in any direction, but may not move into check. The King is one of four possible royal pieces which a player may have. A King may merge with a Bishop to form a Pontiff, with a Rook to form a Dragon King, or with a Knight to form an Eques Rex. If any one of these pieces gets checkmated, you lose. Unlike other pieces, a King may not fuse with another piece by moving to its square. It can fuse with another piece only when the other piece moves to its square.

Dragon King (KR)

The Dragon King moves as a King or Rook, but it may not move into or through check. Although it may not move or capture through check, there is no restriction on its ability to check or attack a piece. The Dragon King is a royal piece and is formed when a Rook merges with its King. When the Dragon King is on the board, it is the player's only royal piece, and the game is lost if it is checkmated. An unchecked Dragon King may split into its components by making a non-capturing move with one of them. The name for this piece is borrowed from Shogi.

Pontiff (KB)

The Pontiff moves as a King or Bishop, but it may not move into or through check. Although it may not move or capture through check, there is no restriction on its ability to check or attack a piece. The Pontiff is a royal piece and is formed when a Bishop merges with its King. When the Pontiff is on the board, it is the player's only royal piece, and the game is lost if it is checkmated. An unchecked Pontiff may split into its components by making a non-capturing move with one of them.

Cavalier King (KN)

The Cavalier King is a royal piece and is formed when a Knight merges with its King. When the Cavalier King is on the board, it is the player's only royal piece, and the game is lost if it is checkmated. An unchecked Cavalier King may split into its components by making a non-capturing move with one of them. It moves as a King or Knight, but it may not move into or through check. Although it may not move or capture through check, there is no restriction on its ability to check or attack a piece. Its Knight leap is considered to follow a certain path. It may begin orthgonally and turn diagonally, or it may begin diagonally and turn orthogonally. This gives it two possible paths to any space it can reach with a Knight leap. As long as the spaces on one of these paths is unchecked, it may complete the move. But if both paths to its destination are checked, it may not complete its move.

The movement of this piece is illustrated with two diagrams. The first one shows its maximal range of movement. The second shows how its movement can be limited by pieces checking some of the spaces adjacent to it. The adjacent spaces are gateways to the spaces it can reach by Knight leaps. To reach a space with a Knight leap, it must be able to pass over an unchecked space that is adjacent to both itself and the space it would move to. There are normally two of these, and if both are checked, the move is illegal. This can be seen in the second diagram. Thanks to the Knight and the Pontiff checking the adjacent spaces in the e file, it cannot leap to any space in the f file. Although the Rook stops the Pontiff from moving to the e file, this does not diminish its ability to threaten check on e5 or d6. Note that even if the Knight were not there, a leap to f4 would be illegal, because it would be moving into check. Thanks to the Knight threatening check in e6 and the Pontiff threatening check on d6, the Cavalier King is blocked from moving to e7. It can reach the other five spaces a Knight could leap to, for it has at least one unchecked gateway space to each of them. In three instances, it cannot pass over the space orthgonally adjacent to it, but it can pass over the one diagonally adjacent to it. In one more instance, it cannot pass over the space diagonally adjacent to it, but it can pass over the space orthogonally adjacent to it. And in one instance, it can reach the space by either path.

Pawn (P)

The Pawn moves as the Pawn in Chess. It moves forward one space, but is allowed a double move on its first move. A Pawn captures by moving one space diagonally forward. If a Pawn makes a double move to a space alongside an enemy Pawn on its fifth rank, the enemy Pawn may capture it by en passant. Upon reaching the last rank, a Pawn may promote to a Rook, Bishop, or Knight. It may not promote to a Queen, Marshall, or Paladin.

Notation

Use algebraic notation as you would for Chess, but use RB for the Queen, and use two letters to designate each of the other compound pieces. For each compound piece, use the two letters for the two simple pieces it is a compound of. Place the letter for the more important or more powerful piece first. So, K goes first for all the royal compunds. Use KR for the Dragon King, KB for the Pontiff, and KN for the Cavalier King. Otherwise, use R first for Rook compounds. So, use RB for the Queen and RN for the Dragon King. Finally, use BN for the Paladin. The use of this notation makes it easier to follow fission and fusion in the game, and it also makes it easier to program on Game Courier. When you make a fusion move, the new piece just combines the two letters for the pieces that fused together. When you make a fission move, just write it as a move by one of the two pieces it is a compound of. It is as though you are playing a game with just simple pieces with rules that permit double occupancy of a space and joint movement by two pieces on the same space.

Computer and Online Play

Zillions-of-Games

If you have Zillions of Games, you may play Fusion Chess on your computer. In March 2001, the graphics and audio were updated. Pictured on your left is the new board used with Zillions. It was made from computer generated textures. In April 2020, the code was updated for the new rules.

• Download fusionchess.zip

Game Courier

Game Courier is our own online server for playing Chess variants. It was created by Fergus Duniho, the creator of this game, and he has fully programmed Fusion Chess for it, so that you can play it with other people online with full rule enforcement.

• Fusion Chess on Game Courier

Vchess.club

Vchess.club is a website created by Benjamin Auder for playing Chess variants online. It allows for live play, correspondence play, and play against an engine.

• Fusion Chess on vchess.club

Similar Variants

Although I came up with the idea behind Fusion Chess on my own, I was not the first to come up with this idea. Pritchard's Encyclopedia of Chess Variants describes some similar games. I was unaware of these games when I created Fusion Chess, and I did not think of these games or borrow any rules from them when I revised it. For the sake of historical interest, here are the games presented together.

Combination Chess (1898)

This game was a century old when I invented Fusion Chess, and Pritchard does not name the inventor. In this game, the Queen moves as a King but isn't royal. As in Fusion Chess, fusion is permissable between any of the pieces except the King and Pawn and with the restriction that no more than three pieces may combine together. This restriction is probably because a Rook/Bishop/Knight compound would move no differently than a Rook/Bishop/Knight/Queen compound. As in Fusion Chess, compound pieces may undergo fission by moving a component to an empty space, though unlike Fusion Chess, a fission move cannot be used to check the King. Castling is not allowed when a Rook is part of a compound piece, probably on the grounds that it is no longer a Rook. Nothing is said about whether castling is once again legal if the other components move away from the Rook.

Coronation Chess (1924)

Invented by Frank Maus. Coronation is the same thing as fusion, and in this game, it is allowed between a Rook and a Bishop after the player has lost his Queen, or more generally whenever the player lacks a Queen. There is no mention of fission in this game.

Union Chess (1924)

Invented by Frank Maus. In this game, coronation is allowed between any pair of Rook, Bishop, or Knight, the only restriction being that the two pieces are different. There is no mention of fission, and no mention of allowing triple compounds like the Amazon. It is not stated whether Pawns may promote to the other compound pieces.

Confederate Chess (1924)

Invented by Frank Maus. This is like Union Chess with fission, which is described as abdicating a coronation. Perhaps the name for this game came to mind because the Confederacy wanted to secede from the Union. There is no mention of any restriction on fission. So, maybe fission can be used to capture a piece.

Empire Chess (1925)

Invented by Frank Maus. This is like Coronation Chess with the additional options of combining Rook and Knight into an Empress or Bishop and Knight into a Princess. As in Cornonation Chess, coronation is allowed only after the Queen is lost, or more generally, when a player does not have another compound piece on the board. But a player may gain additional compound pieces through Pawn promotion. A Pawn may promote to an Empress or Princess, though a player may never have two compound pieces of the same type on the board at the same time.