Charybdis Square is played on an 8x8 uncheckered square board, with 8 additional black or white squares adjacent to each side. Along any side, either one or both colors may be present, resulting in two different boards. On these squares there are white and black stones. These stones are fixed (since they could not even be captured if they weren't) and therefore, perhaps unnesessary, marked as such. Though they are never part of any group in the 64-squares playing area, they do play a role in capture.
The original game is a hex version, known as Charybdis.

Rules
There are two players, Black and White. Both have a sufficient number of bi-colured stones, black one side, white the other. The game starts on an empty board. White moves first after which turns alternate.
Definition: a group consists of one stone or two or more like colored orthogonally connected stones.

On his move a player must either:

• Grow any or every of his existing groups by one stone, or ...
• ... put a stone on a vacant cell, not orthogonally adjacent to a like colored group, thereby creating a new group.

Capture
Capture can only take place in a 'growing move', not by placing a single stone. It follows the custodian method, best known from Othello, but only in the four main directions (i.e. not along diagonals). The act of enclosing a straight unbroken line of the opponent's stones between stones of the moving player, effectuates the capture and immediate reversal of the enclosed stones. The fixed black and white stones along the edge can be used for enclosure as if they were ordinary stones.

• The only restriction on single placement is that the stone may not be placed adjacent to a like colored group. It may be placed adjacent to an opponent's group or groups, but any custodian enclosure it may thus make does not result in a capture.
• Using option one, a player may grow one stone at any or every of his existing groups. If he connects two of them with a single placement, the resulting group may grow no more in that turn. Two groups may be connected by growing both of them, as long as both placements only touch one another, but neither placement is adjacent to both original groups.
  If growth results in one or more of the opponent's stones to be enclosed in the custodian fashion described, these are immediately reversed, to unite their captors in one group. Such a group may grow no more in that same turn. However, other groups may still be there that have not yet used their option to grow, and these may still grow and/or capture, using, if possible, the stones that were previously captured, to enclose more stones.
  Note that large captures result in large groups, with restricts growing and capturing options in the subsequent turn. This negative feedback should be kept in mind.

Object
Not surprisingly we're going for the largest territory here. The board has 64 squares, none of which are safe, and draws are possible, but unlikely.

Another object
Of course players may agree that, all things being equal, the player who first connects opposite sides of his color with an orthogonally and/or diagonally connected chain in his color wins. In the variant where black and white are present fourfold along the sides, connecting three like colored sides, also counts as a won position. Diagonal connections may cross one another, but since the first player to complete a chain wins, draws are not possible.


Charybdis Square © MindSports
No applet