Once I played a game against a 9 kyu in our club, with whom the handicap usually varies between 5 and 7 stones. He took Black and no handicap but had two special stones. One, marked with a triangle, when played, enabled him to play once more before White's turn. The other stone, marked with two eyes, did what it appeared to do: it was alive.
He thought that either of them already made up for the handicap, but I thought that I could even deal with giving him a living group and two moves in a row.
How wrong I was. What I had severely underestimated was the power of the threat of those stones, without them being actually played. I found myself playing so conservatively, that at some stage, he was getting ahead before having played any of his special stones. So I started playing more aggressively, but in the middle of a fight, he cut off my pivotal stones with his two-eyed stone, and I resigned at the sight of two consective moves capturing my large group.
While Black can simply play proper Go, White has to play counterintuitively and anticipate a large loss at any time of the game. It is not really a good exercise to learn Go, but it is lots of fun. We haven't repeated the experience since.
Some other ideas for special stones:
- A converter stone, that is played in place of an opponent's stone. This could be interpreted that you take the opponent's stone as a prisoner, or give it back to them.
- A switch stone that, once it has been played, the player can use a later turn to switch that stone's position with an oppenent's stone
- An "eyelid" stone, that could be played to fill in an eye of an oppenent's living unit (meaning true immunity would require 3 eyes for the oppenent)
- A peep stone, like the stone that allows you to play 2 in a row, but more limited, in that you can peep and cut in the same turn (very powerful against half-bamboo joints)
- A Lifeblood stone, instantly makes any unit it is connected to alive, but cannot be played in connection and is not immune unless part of a group (giving the opponent a chance to cut after it is played)
- A reach stone, that can be played with a one space gap between it and another stone/group, but is considered connected to that stone/group even if the opponent plays in the gap.
- A slide stone, a stone that, after being played, the player can use their turn to slide it (move it along the board, horizontally or vertically, until another stone obstructs its path. See my addition to Reuse Go for more info on sliding)
Illich: What about these special stones:
- opponent's stone - black can place white stone and vice-versa (good for stealing an eye - so the opponent needs to make three eyes instead of two, if you have this special stone...)
- 2x1 stone (useful for cutting or escaping)
KarlKnechtel: This has set my mind in motion for sure - how about DominGo, where all stones are 2x1? Tetris stones seem a big too chunky for this sort of play, but 2x1 stones have some interesting properties.
- tetris stones - shapes made of four stones, it might be interesting when both players have some of these
- taboo stone - opponent cannot place his stone next to this one
Some ideas for play:
- Set a price n on each stone, so that at the beginning of the game each player can buy the special stones by giving n komi to the other player, or instead of komi use handicap and adjust the prices accordingly
- Randomly allocate some or all of the above stones at the beginning of the game (drawing them from a bag, etc.)
(This would be difficult to do with tetris stones, no? Maybe draw the shape on the stone, and when it is played the player adds three normal stones to complete the shape.)
- Create some scenarios in which black gets some of the stones and white gets the others. Write these scenarios so that they make sense, putting a "story" behind the game. (eg. white gets stones that make life, black gets stones that kill)
KarlKnechtel: "scenarios" are worth combining with unusual gobans representing world maps... you could recreate historical battles (I'm imagining a "Plough salt into the ground stone", which when played removes orthogonal stones from play along with the intersections themselves, and which remains alive as a special provision since it can't be surrounded - maybe you could get one as a bonus for capturing a one-eyed group?), or concoct some fantasy setting (black and white stones seem perfect for Orcs vs. Elves!).
http://www.di.fc.ul.pt/~jpn/gv/pieces.htm has further ideas for special stones.
Historic Three-Color 10x10 Go at Matsumoto Castle appears to involve the use of black, brown, and white stones.