Iisō Sanshun

[or2az]

Got this interesting hand yesterday. I knew San Renkō (Three Consecutive Pungs) was an optional yaku not used in this game so when a was discarded, I called chi instead of pon thinking that the chow based hand might be worth something, but it wasn't. All I got was tanyao. Bummer!

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Turns out this was also an optional yaku not used in this game and is called Iisō Sanshun (Pure Triple Chow).
In fact, this yaku wasn't even listed in another game which does allow San Renkō even though they seem to be the exact same thing (in a concealed hand). However, I did find it in Barts guide (p.57), and here : http://mahjonginmame.com/yaku.htm
There are a couple of minor differences.
For instance, is it sanshun or sanjun. Or both?
Also, when concealed (and valid, if ever), is it 2 han or 3 han?
(If 222333444 is exactly the same as 234234234 in a concealed hand, why should one be 2 han and the other 3 han?)

One thing is for sure, it's a valid chinese mahjong hand. I guess you can't win 'em all.

[Ignatius]

This yaku, 一色三順 Iisô San Shun can also be called Isshoku San Jun, the name I knew. And it's like a San Ren Kô.

When this kind of combination it's considered as three runs, minjun or whatever you call it, usually has to be menzen, without calls. Some rules allow you to call tiles. Which make it just like the San Ren Kô .

[Referee]

Isshoku Sanjun Pinfu = San Renkou San Ankou. (So, basically, you invoke the Choice Principle of Maximum Score)
I don't recognize neither of those two in my games, anyway.

[Barticle]

In terms of optional yaku/yakuman you will encounter the following in a few video-games: open riichi, san/suu renkou, renhou, shiisan puutaa, dai sharin and paa renchan.

It's very rare to see any others - and whenever optional yaku are available there'll usually be a rule option to toggle them on/off that gives a list.

As with all things mahjong, there are exceptions. I've played a couple of titles recently that had some very exotic options but lacked the more common ones above.

[Iapetus]

Isshoku Sanjun Pinfu = San Renkou San Ankou. (So, basically, you invoke the Choice Principle of Maximum Score)
I don't recognize neither of those two in my games, anyway.

You could ron on the san renkou and the triplet would be open so no san ankou, so it's not impossible.

But mostly this is a yaku in MCR. There's all sorts of crazy stuff there you could invoke as optional yakus in riichi.

[Referee]

That's correct. Note that the other one doesn't guarantee Pinfu, either.