This variant is inspired by @bugcat’s recently proposed Quartered Go and Ultimate Tic-Tac-Toe.
Like Quartered Go, it is also played on an even-sided board (e.g., 12x12, 16x16, or even rectangles like 14x18), which allows for the board to be cleanly divided into four equal quadrants. The top-left quadrant is called the “odd-odd” quadrant, the top-right is called “even-odd”, the bottom-right is called “even-even”, and the bottom-left is called “odd-even”. Each move chooses which quadrant the next move must be played in, based on whether the coordinates of the move are even or odd.
Here’s an example game to illustrate
- Black is free to place their first move anywhere and chooses to play at 10-4, which is “even-even”.
- White must play in the bottom-right quadrant and chooses to play at 9-9, which is “odd-odd”.
- Black must play in the top-left quadrant and chooses to play at 3-3, which is “odd-odd”.
- White must play in the top-left and chooses to play at 4-4, which is “even-even”.
- Black must play in the bottom-right and chooses to play at 10-10, which is “even-even”.
- White must play in the bottom-right and chooses to play at 9-10, which is “odd-even”.
- Black must play in the bottom-left and choose to play at 4-9, which is “even-odd”.
- It is now White’s turn and they must play in the top-right quadrant.
Technicalities
- The first move of the game can be played anywhere.
- Instead of playing a stone on the board, a player may choose to pass, but that gives their opponent the freedom to play anywhere on the board for their next move.
- The game ends when 6 consecutive passes happen (e.g., black passes, white passes, black passes, white passes, black passes, white passes OR the similar sequence starting with white).
- Stone scoring: the winner is whoever has the most stones on the board when the game ends.
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Ultimate Demarcated Go
This related variant is similar to above, except it is played on a 9x9 board divided into nine 3x3 regions.
Each move determines the region that the next move must be played in according to the following pattern:
Here’s an example game to demonstrate:
- Black can play their first move anywhere and they choose 6-5, which is in the “middle-right (6)” of that 3x3 region.
- White must play in the middle-right (6) region and they choose 8-6, which is a “bottom-center (8)” move.
- Black must play in the bottom-center (8) region and they choose 5-7, which is a “top-center (2)” move.
- White must play in the top-center (2) region and they choose 4-3, which is a “bottom-left (7)” move.
- Black must play in the bottom-left (7) region and they choose 3-7, which is a “top-right (3)” move.
- White must play in the top-right (3) region and they choose 7-3, which is a “bottom-left (7)” move.
- It is now Black’s turn and they must play in the bottom-left (7) region.
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May I call it “Sudoku Go”? 
This could be generalised for play on an N^2 x N^2 board.
I’d love to try it!
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Oooh, I’ve always liked the idea of Ultimate Tic-Tac-Toe, but the gameplay was just confusing to me. Maybe Ultimate Demarcated Go is what I’ve been waiting for!
If you have no legal move, are you forced to pass? I think in Ultimate Tic-Tac-Toe you get to play wherever instead if you were supposed to play in a decided board, right? Maybe the second option is better balanced.
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I believe this is implicitly what follows from the rules, and probably also the reason why the game only ends after 6 consecutive passes?
I’m not sure why 6, and not 3 consecutive passes…
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“The rules of Demarcated Go are so elegant, organic, and rigorously logical that if intelligent life forms exist elsewhere in the universe, they almost certainly play Demarcated Go.”
—@yebellz (probably)
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This was my original intention, however, you are probably right about balance:
I’m not so sure either. I just wanted to be sure avoid some weird things about ko, but I think you’re right that 3 may be sufficient. As for ko, I think a basic positional superko rule would be okay.
Anyone want to be guinea pigs for a test game? Perhaps @martin3141 and @le_4TC would be willing to experiment yet again?
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Maybe Ultimate Demarcated Go has too many regions. Consider the following line of play:
Note: Black’s first move is at E5 (captured) and White is forced to play move 18 at E5, making an awkward 3x3 shape. The exact ordering of these moves may be different, but the same position can always be forced by Black.
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This may indeed be a problem in Sudoku Go, although I’m not sure how to evaluate the resulting position to be honest. To avoid this kind of forced opening, perhaps one “destination region” should include multiple “route regions” like in Demarcated Go:
For example the game could be played on an 18x18 board with 9 regions of 6x6 made of 4 3x3 patterns. Unfortunately it would not resemble ultimate tic-tac-toe as much.
Sure, I would happily play with all of you great people 
Go variants are so much fun!
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I’m interested in playing too
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