The Chess 
Variant Pages

Twelve Mutation Chess

or Twelve Mutations on a Chessboard

This variant is based on the idea that one or more 'mutators' (rules that modify a chess game in some manner) may be activated/deactived in a chess game at any one time. These mutations are in the form of additional rules (or rule modifications).

For the purposes of this document, there are 12 mutators, but certainly other mutators could be used. For the twelve mutators specified below, 12 markers are created with the mutator names on both sides. One side of the marker should have the mutator name with a line through it.

Before the game starts, the players take turns (starting with black) placing mutation markers, crossed-out side up. The suggested squares for allowing the markers to be placed are:

a4, a5, b4, b5, g4, g5, h4, h5

In the suggestion above, only 8 markers are placed, but players may place an even number of markers between 2 and 12 if they wish.

The game then starts, initially using FIDE chess rules.

When a player moves one of their non-pawn pieces off of a square that has a marker on it, the marker is flipped over. If the marker is flipped over to the crossed-out side, the mutation rule is deactivated. If the marker is flipped over to the non-crossed-out side, then the rule specified on that marker is activated (ie. goes into effect).

Important note: Whenever a mutation is activated or deactivated, the rule changes don't go into effect until the current player's turn is over. Then immediately before the other player's turn, the rule changes go into effect.

The Mutation markers

  1. Atomic

    When a piece is captured, the capturing piece and all pieces that were adjacent to the captured piece are removed from board. King captures are exempt from this rule (ie. When the King makes a capture, only the piece captured is removed from the board). Pieces removed from marker-squares do not flip the marker.


  2. Attack

    Players must make a capturing move if possible.


  3. Avalanch

    Each turn a player makes their normal move, then must push (non-capturing move) an opponent's pawn forward one square. The pawn push is compulsary, and may only be skipped if such a push is not possible. The initial two-square pawn move rule does not apply. If a pawn is pushed to the last row, the player owning the pawn decides what piece it is promoted to.

    The pawn push may not be used to block check. The King may not be left in check before the pawn push (ie. the move before the pawn push must be a legal chess move). If the player's only pawn push option puts his King in check, then the position is considered check-mate.


    Avalanch Chess was invented by Ralph Betza.

  4. Berolina

    All pawns move like Berolina pawns (which capture straight forward, and make a non-capturing move diagonally forward).


    See the Berolina Chess page. The Berolina Pawn was invented by Edmund Hebermann.

  5. Cannon

    All Rooks move like Paos (cannon), all Bishops move like Vaos.

    Interactions: none.

  6. Dice

    Players roll a d8 (eight-sided die) before moving and attempt to move one of their pieces located on the rolled row or column (a=1, b=2, etc.). If the player is unable to move such a piece, then the player may make an unrestricted move.


    This mutator is based on a variant by Fergus Duniho, in which the player must move a piece on the rolled column, and the object is to capture the opponent's king.

  7. Drop

    When a piece is captured, the capturing player retains the piece and may drop it (to a vacant, non-marker square) on a following turn. The drop replaces the normal move. Players may not drop pawns on last rank or on marker squares. Promoted pawns revert to pawns when captured.

    When the Drop token is deactivated, all pieces currently available for dropping are no longer available to be dropped, even if the Drop token is subsequently activated. Pieces captured while Drop is not active are never available to be dropped.


  8. Equus Rex

    Kings move like Knights in addition to moving to adjacent squares (Equus = Horse, Rex = King).


    The name "Equus Rex" is based on the King+Knight piece mentioned as "Eques Rex" on Fergus Duniho's Fusion Chess page.

  9. Monochromatic

    Pieces must stay on same color squares. Knights move like Camels. Pawns move two squares forward (non-leaping). Kings are allowed to also move like a Dabbabah (ie. a (0,2) leaper). Pieces may still give check even though they can't move to the square.


    See our Monochromatic Chess page.

  10. Non-Prise

    Queens, Rooks, Knights, and Bishops cannot capture each other (ie. a piece that is not a pawn or King may only capture pawns or check a King).


    Non-Prise Chess was invented by Bruce Zimov.

  11. Rider

    All Knights move like Nightriders.


  12. Swap

    The player may swap positions of a piece with another friendly piece that it covers. Pawns in the first or second row may still move two squares, even if they have previously moved. A non-pawn piece swapped off a marker does flip the marker. It is possible to flip two markers at once with this type of move.

    Note that only one swap is allowed per turn.

    Interactions: none.

    Influenced by Joao Pedro Neto's Swap Chess and the mutator he mentions on his Mutators page.



This game is not for the faint of heart. Remembering which mutators in are effect at any one time, along with handling the interactions between the mutators is quite mentally challenging. For those interested in a wildly unbalanced game of shifting fortunes, this variant may have some attraction. The interactions between the mutators can lead to some novel and amusing situations. For those interested in a quiet, leisurely game, I wouldn't recommend this.

Thanks for Fergus Duniho for helping to playtest this game and for suggestions and corrections.

Standard Mutator Form

For a discussion of mutators, see Joćo Pedro Neto's Mutators page. The mutators used in this game might be said to be 'dynamic' in the sense that they they can be activated and deactivated in the course of a single game.

Using Joćo Pedro Neto's notion of mutator parameters, we may specify the parameters for a generalized version of this game as:

FIDE[NMutation](C, {M}, {S})

where: C is the number of markers to be placed
       M is a set of dynamic, compatible mutations
       S is a set of squares upon which mutation markers may be placed

So this particular game would be:

FIDE[NMutation](8, {[Dice][Avalanch][Swap][Attack]
                    [Equus Rex][Monochromatic][Non-Prise]}, {a4 a5 b4 b5 g4 g5 h4 h5})

Written by David Howe.
WWW page created: March 31, 2000.