The Genius, by A Skymin’s Mind #3

Tactical Yutnori

Used as Death Match of Season 1, Rounds 3, 4, 10, and Season 4, Round 2.

Rules

Basic yutnori rules apply, as follows. Wikipedia is also pretty complete.

The game uses a special yutnori board. Players cast yut sticks which can be “up” (plain) or “down” (marked). There are thus four sticks cast. The number of up sticks is the player’s score: one up stick is 도 (do), scoring one space; two up sticks is 개 (gae), scoring two spaces; three up sticks is 걸 (geol), scoring three spaces; four up sticks is 윷 (yut), scoring four spaces; and no up sticks is 모 (mo), scoring five spaces, unlike the others. In addition, yut and mo also allow the player to cast again, thus possibly accumulating several yuts and mos before a different cast is thrown.

Each player has two pieces on the board. After a move, the player can move any of their pieces for the score cast. In case of yuts and mos, they can choose where each cast goes to, but a cast can be only used for one piece. (For example, with a yut and a gae, one can use them to advance a piece six spaces (4+2) or a piece four spaces and another two spaces, but not split them into three and three.)

Normally, pieces travel along the outer edge of the board. However, when a piece lands on a corner or the center of the board, it has the option of following a different, shorter route. Note that the piece must land on the corner or the center to allow the alternative route; simply passing by doesn’t count.

When a piece lands on another of its own, the two may decide to merge and continue together. When a piece lands on an opponent’s, the opponent piece is returned back to home and the player gets another cast. (It seems that if one gets a yut or a mo in this new cast, it doesn’t give another cast.) A player wins if they get both pieces back to the home after circling the board.

That concludes yutnori rules. However, as this is a tactical yutnori, additional rules are in place.

The two Death Match players each chooses a partner. The partners also play, but they cannot win. Each player holds two sticks, one is “up” on both sides and one is “down” on both sides, and each throws one stick of their choice. (Teammates may discuss, of course.)

In addition, there is a variant called “back do”. If one gets a do, instead of advancing by one space, a piece is retracted by one space. (If one doesn’t have any piece on the board, the turn is skipped.) Note that this allows a piece to retract back to home and beyond by back dos, and it’s still counted as circling the board.

Strategy

Oh hey, a board game. I don’t know the strategy of playing yutnori at all. However, I do know some strategy for casting the sticks.

We can denote a couple of “good” moves:
– A move that captures a piece is almost always good, because the piece is captured and one gets another cast.
– A yut or a mo cast is almost always good, because one gets another cast.
– A back do that brings a piece to the “blind spot”—the space right after the starting point—is quite good as it’s immune to capture except by another back do from a piece two spaces after home, and that it is just two more back dos to win.
– A move that gets to a corner is pretty good, as it allows a shortcut. When an opponent piece is at the corner, this is especially powerful.

With the above moves, one can decide which casts are good.

If only one of the five casts is good and it’s not gae, one can easily stop the cast as they control two sticks. For example, if a geol is good, it needs three up sticks, so one can simply play two down sticks to prevent this. (Gae is special: it cannot be prevented, only its chance minimized by playing two equal sticks.)

However, when more casts are good and they are not all countered together (for example geol and yut are both countered by two down sticks, so this pair doesn’t count), one gets to a dilemma. Which cast should be prevented? A smart player can determine which of the casts is the most likely to be prevented by the opponent, and hence can predict what the opponent is going to play, and hence what their play should be to give the other cast. For example, one might want to prevent a geol to avoid having their piece captured, but this means two down sticks. The opponent, if they are smart, can play two down sticks too, to allow a mo and another turn. (Of course, reverse psychology can kick in; one might intentionally allow a geol to avoid the opponent garnering mos.)

When there is no particularly good move, the second point above almost always applies. A yut or a mo is very effective, and thus one might want to play an up stick and a down stick to prevent it.

Another strategy, now being a strategy or circling and not a tactic of casting sticks: position the partner’s piece properly so that they can be used as hopping stones. Be careful not to make them hopping stones for the opponent!

That’s all I have, I suppose. Any other opinions?

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2 thoughts on “The Genius, by A Skymin’s Mind #3

  1. The landing in the corner to go inwards I missed in the original plays, so thanks for that. Do you also need to hit the centre dot to change direction, or is it a free for all when you’re inside?

    While some of the assistant players acted as stepping stones, I seem to remember assistants hanging back to give chase to pieces out of the gate, which seemed at the time to be the main reason the game dragged on for an eternity. I can see the allure but it makes for lousy gameplay, and I couldn’t see a non-radical fix for it that didn’t involve staggering entry.

    I agree that, by far, the most interesting thing in the adaptation is replacing chance with polling. Is it now solvable? Are there still squares that are more useful under this approach as in most roll-and-moves which offer benefits for exactness, or does the format change democratize them? I also don’t have a good grasp on whether the casting choice is subject to min-maxing telescoping. Like, A’s the worst thing they can throw at me, so the best I can do with that is X, but if they expect X, then they can throw B at me which is then worse, so I need to actually throw Y, which is optimal against B, which they also expect so… I feel that it’s probably foolish in this implementation and more useful in the other application of the poll-as-die mechanic in Series 2, but I can’t actually present a backing argument. Is there a name for this mechanic in the literature? Failing that, has it seen prior use in board gaming? I think it’s fair to say the mechanic intrigues me 🙂

    Reply
    • Yes, you need to hit the center dot to change your direction from top-right-to-bottom-left to top-left-to-bottom-right, but this only happens if you take the first shortcut (first corner at top-right to go to the center). Wikipedia has a sufficiently good entry about this.

      That’s a good point. However, seeing that the Death Match players take their turns exactly after their respective teammates, the best strategy I have in mind is to get a friendly piece on square two after home, so one can step on them and then go further (or get back do) to avoid immediate hit by the opposing supporter.

      Regarding which squares are good, I don’t think there’s any difference, as one doesn’t involve chance in my good squares. For example, capturing an opponent is good, and there’s an opponent three squares ahead, so I want to make this throw to score a three. Regarding how precisely, that’s the psychology part.

      Regarding your “min-maxing telescoping”, I’m not sure what it’s called, although I know what you refer. This appears more than just in board gaming; this appears in pretty much the entire game theory. Any game where there are simultaneous player actions will have this. (This also means chess and the like don’t, because only one player decides each turn and thus the opponent knows the choice before selecting his.)

      Reply

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