One device, passed between you. Player 1 opens, then Player 2 chooses to swap or stay.
Classic ladder
Each level is a stronger computer. Pick any board size for each game; beating a level on any size opens the next one.
Classic rules
The opener places Blue's first box. The other player then chooses: swap and take Blue with that box, or stay and play Coral. This is the pie rule, so neither side gets a free edge.
Blue plays from the left and Coral from the right. Coral's first box must land to the right of Blue's, and Blue moves first after that.
After that, each turn is 3 boxes. You can't place behind your own first box.
Loose boxes are vulnerable. Four joined in a T, L or square become a cluster. Straight lines and zigzags don't count.
A group is eaten when every forward and sideways side is covered by the opponent. Its back doesn't need covering, and edges are ignored.
A cluster can only be eaten when it's covered by clusters, and the biggest one touching it is bigger than it is.
Eaten boxes flip to the attacker's colour and join their clusters.
A safe space is a 3 by 3 space walled in on all sides by your clusters. Edges can't be part of the wall, and your opponent can't place inside it.
Fort pieces can only go in the ring of your safe space and use your 3 placements. If the wall breaks, they turn into normal boxes.
The king is free. It goes in the centre on a turn after the ring was finished, and it wins at once.
If neither player has room left to make a safe space, the player with the biggest cluster gets the space clearer. If the biggest clusters tie, the game is a draw.
The space clearer clears a 3 by 3 space starting where you place it and running forward. Fort pieces and the king go there, and no wall is needed.
The opponent can still place in the cleared space if it's in front of their first box. If it's behind their first box, it's a clean shot.
If nobody can place at all, the game is a draw.
Rat and Cat rules
The board starts empty on 9 by 9. Each turn is 3 boxes on any empty frame.
The opener plays Blue's first turn. The other player then chooses to swap and take Blue, or stay and play Coral.
Clusters work as in Classic. A group is eaten when every side is covered by the opponent, and edges are ignored.
The player with the bigger biggest cluster is the cat, and the other is the rat. If those are equal, more boxes decides. Roles can swap.
At the start of your turn, if your opponent holds 80% or more of the boxes, you roll for an expansion box: 1 in 6 at 80%, 1 in 4 at 85%, 1 in 3 at 90%, 1 in 2 at 95%, and certain at 100%. You can hold one box, and rolls start once 12 boxes are on the board.
When no empty space can hold a T, L or square, the rat uses their held box. With no box, or with the board at 13 by 13, the rat loses.
On a tie, the player with the next move has a 1 in 3 chance of an expansion box. If it misses, the game is a draw.
The expansion box goes just outside an edge and adds a T shape of 4 new frames. Using it on your turn costs no placement.