1 Game Board, a 5x5 grid. The rows are labeled 1 to 5 from bottom to top while the columns are labeled A to E left to right. So the lower left corner is A1, the center is C3, and the top right is E5.
25 two sided tokens, with one side being "light" and the other side called "dark".
How to play
Players take turns and can not "pass". During a player's turn they select a legal square (see below) and modify the square selected as well as the ones directly above, below, to the left, and to the right in the following way:
If the square is empty, add a token with Light side up.
If the square has a token with Light side up, reverse it so the Dark side is up.
If the square has a token with Dark side up, leave it alone.
After updating the board the player checks for runs of 5 consecutive squares each with a token with the Dark side up. This could be a row (such as A2 to E2), a column (such as B1 to B5), or one of the long diagonals (such as A5 to E1). If such a run is made, the player is awarded a point and the 5 tokens are removed. If more than one run is created on the same turn, the player gets a point for each and all tokens in each run are removed.
There are two restrictions to which squares a player may select for his or her turn. They may not choose a square which already contains a token with the Dark side up. And the player may not choose the square their opponent did on the turn before.
Play continues until one player scores 5 points.
Sample game
Player 1
Player 2
B2
C1
A2
A4
B5
E5
C4
D1
C4
At this point Player 1 is awarded a point for completing a run of 5 in the C column and the tiles are removed.
Variations
Multiple players - Due to players sharing the same board and tokens, Syncro can easily be played by 3 or more players without changing the rules at all.
Large boards - Players can decide to use a larger board such as 7x7 or 9x9, while adhering to the rule of looking for a run of 5. Larger boards allow for a slower game, so it is suggested you lower the number of points required to win.
Cut throat - Instead of playing to 5 points, the first player to make a run of 5 wins.
