BRIEF DESCRIPTION: This is a game where two populations compete for survival. Pieces have gender, can 'mate', give birth, age and die. The game is won by the player whose population lives longest or who connects two sides of the board. The unusual theme of the game keeps it fun whilst also enabling considerable strategic variety and depth.

BOARD AND PIECE DESCRIPTION: The game is played on a 6x6 board. One player is Copper, the other Teal. Male pieces are represented by triangles, females by circles. Each piece also has a number written on it. This is the piece's remaining life turns (lifespan) i.e. number of 'turns' left before it dies (higher numbers meaning greater longevity). The remaining life reserve for both players is displayed on the left side of the board. The life reserve is the supply of life turns that can be drawn from and allocated to pieces that a player introduces to the board during the placement phase.

TURNS: There are four phases in each 'turn' (the last two phases being automatic):

1. Placement/Movement - Each player either places a new piece on the board or moves an existing piece.
2. Birth - Each player gives birth, if they wish, anywhere where the conditions for birth are met.
3. Ageing - All pieces age (their remaining life turns are reduced by one).
4. Death - Pieces that have no life turns left will die (disappear), and any player who has met one of the objects of the game wins.

OBJECTS: The game can be won in either of two ways both assessed only after the ageing/dying phase of each turn:

1. If one player is the only one with pieces left alive. This includes the other player having no reserve life turns (so a player is still alive if they have no pieces on the board provided they have at least one reserve life turn left to make a placement in the following turn.)
2. By one player connecting two sides of the board through a continuous series of their pieces which are all orthogonally connected. For Teal, this will be connecting the two vertical sides, for Copper, top and bottom.

Please refer to 'reaper.pdf' for complete game instructions and examples.

Note: Grim Reaper is playable as a PbEM game at Super Duper Games: http://superdupergames.org/

NOTES ABOUT THE PROGRAM:

• When placing new pieces, the choice of available life turns of the pieces is restricted (e.g. typically 5 or 3). This is a slight deviation from the rules which was done in order to reduce the number of choices and thereby improve the effectiveness of the AI.

• In some cases it is possible for multiple mothers to give birth at the same position. In that case, the program will pop up a menu that allows the player to select which mother is to give birth. This is an important distinction because females can only give birth to one piece each birthing time.

• As of this writing, Grim Reaper is the most complex Axiom game. Because new pieces with varying life turn values can be dropped on the board and existing pieces can move, the game has a fairly high branching factor. In addition, the dual goals of survival and connection along with the need to manage life turns and the many phases, meant that developing a competent AI has been a formidable challenge. At one point during its development a neural network based evaluation was tried (See GRNN.jpg to view the network architecture). The neural network was constructed by creating a population of genetically evolving neural networks which played against each other in hundreds of tournaments. The fittest networks survived and were transplanted into the program. Although, this approach yielded a stronger opponent than the initial hand-crafted AI, an even stronger AI was eventually developed by hand tuning the evaluation weighting factors and testing play strength via the AutoPlay program. What we found with the neural network was that one net would manage survival well while another net would be good at connecting, but we never managed to find a single net that was good at managing both goals.