Serpent 2025

Serpent is a drawless exnihilation game for two players: Black and White. It is played on the hexes (cells) of an initially empty hexagonal board. The recommended size is 5 cells per side, although 4 and 6 are also valid. Each player has a sufficient supply of stones of their own color.

Definitions: A snake is a maximal set of connected stones of the same color, whose stones are adjacent to no more than two stones of that snake that are not adjacent to each other. A single stone is an egg. The length of a snake is the number of stones it contains. An end is a stone of the snake that is adjacent to exactly one stone of the same snake. The head of a snake is the end with the shortest survival path to the end or egg of another friendly snake. The other end is the tail. If both ends have survival paths of equal length, either one may be the head and the other the tail. A survival path is a continuous sequence of empty cells from an egg, head, or tail of a snake to an egg, head, or tail of another friendly snake, such that, by filling the sequence and the ends with friendly stones, a single valid snake would be created. An egg or snake is alive if it has a path to survival to another friendly snake's egg, head, or tail; otherwise, it is dead. An egg or snake is also alive if there has never been more than one egg or snake of its color on the board. A hostile terrain is a maximal set of connected empty cells with no survival paths for one or both players.

Turns:Black plays first and then turns alternate. On your turn, perform one of the following actions:

Place a stone of your color on an empty cell adjacent to at most two friendly eggs and to no friendly snake. Move a friendly snake's tail to an empty cell adjacent to its head. The move is valid only if, after all the removals, the snake maintains a shorter survival path than the previous one, which can reach 0 cells in length.

At the end of your turn, choose a color and simultaneously remove all of its dead eggs and snakes, then do the same for the other color. A removal is valid only if it creates hostile terrain for the owner of the removed stones until the beginning of their next turn; otherwise, the formation of such dead eggs or snakes is illegal. If the only stone removed is the one you just placed, that placement is illegal.

End of the game:You win if the last enemy egg or snake is removed from the board.

—description from the designer