By Jörg Knappen
A crossover between chess and the computer board game Ataxx (also known as Blobs, Infection, or Spot).
The board and the pieces
The game is played on a standard chess board using two sets of standard chess pieces. Each player gets one colour from one set of standard chess pieces, the second set is needed because pieces can be converted to the other colour.
The pawns do not move as FIDE chess pawns, but as Ataxx Soldiers: They can jump to any square two squares away from the starting square. A piece with this pattern of movement is known as Centurion (see Archchess) or Squirrel (see piecoclopedia).
The starting setup
White places a king on a1 and a knight on h8, black places a king on a8 and a knight on h1.
Starting with white, the players play alternately. A move consists of either:
(a) dropping a new piece of one's own colour on a square adjacent to another piece of one's own.
(b) moving a piece of one's own colour according to the rules of Chess (with the exception given above) to an unoccupied square.
After the move, all pieces of the opposite colour adjacent to the piece moved or dropped are turned to the colour of the player who has just moved.
There are no captures.
There is Zugzwang; it is illegal to pass a move unless one has no legal moves left. In this case, the other player may add more moves or drops, until the end of the game is reached.
Aim of the game
One wins the game by either:
(a) Converting the opponent's king.
(b) Enclosing the opponent in such a way, that he occupies the minor part of the chess board.
The game ends, if after the last drop there were 50 moves played and none of the players can claim a win, or if a repetition of positions occurred.
Note, that this end of the game does not count as a draw. Instead, the game is decided by the area count -- consisting of the number of pieces of a colour and the number of free squares enclosed by them -- decides the game. Free squares not enclosed by pieces of one colour are neutral and do not count for either party. In rare cases, it may come out as a draw.
A note on tactics
The stock of pieces to be dropped is limited, such that half of the chess board always remains empty. This enable the classical chess pieces to move around, although they loose strength as the board fills up.
A drop is a very strong defensive move, try to keep a piece to be dropped as long as possible.
In the beginning, white has forcing moves against black. It seems, that it cannot force a win with these moves. For those uncomfortable with the situation, here is a variant:
Variant: Balanced Schataxx
In the first five half moves (first and second moves of both colours, third move of white) it is not allowed to drop a queen or a rook.
Variant: Schataxx with unlimited stock
The stock of pieces to be dropped is extended by more Ataxx soldiers such that there are always soldiers left for dropping. This way, the board finally is completely filled.
A concise site with information on Ataxx/Blobs/Infection/Spot can be found under:
http://www.pressibus.org/ataxx/indexgb.html (in english)
There are other chess variants with conversion, e. g. Conversion Chess.