I recently played two hanchans on Tenhou that taught me some tough lessons. Having memorized the yaku and getting a feel for the game, I now have the play style of going for “mentanpin” (menzen tanyao pinfu) all the time. I’ve started watching some JPML (Japanese Mahjong League) matches on YouTube https://www.youtube.com/channel/UCqHDeUer8bgaqswSuFP7FxQ and from what I’ve gathered riichi and pinfu are the foundation of Japanese mahjong. However these two hanchans recently showed me that I was being too narrow-minded.
Kokushi Musou aka the 13 Orphans
This hand is a yakuman and contains one copy of the 13 terminals and honors plus a duplicate of any. Although this hand is rare, it does happen occasionally often when least expected. Recently I dealt into a Kokushi by playing a pei around the 14th turn. For me who was thinking pinfu constantly, this was even more surprising. Now I always look for the signs of Kokushi in the discards. Kokushi can usually be identified by a lack of terminal and honors played early on. The discards should have an abundance of middle tiles like 4,5,6. Usually a Kokushi tile will flow out somewhere in the middle, but in rare cases one will not and the Kokushi will be harder to detect. If the dora is not a Kokushi tile, dealing a dora is usually a strong indication of going for a big hand. Just remember: Kokushi Musou happens and you should never dismiss it as a possibility.
For some statistics on Kokushi Musou, check out Umaikeiki’s article here.
Nagashi Mangan is worth mangan and is achieved by having your discard pile contains only terminal and honors when there is a draw game and no one has called any of your discards. In the game above, I started South seat. If you watch East 2, the player across from me got a Nagashi Mangan. I was very surprised by this because 1. I didn’t know that Tenhou had Nagashi and 2. I hadn’t even considered Nagashi in the realm of possibilities. Unfortunately I was dealer and riichi’d so I had to pay the dealer penalty and couldn’t have done anything even if I had noticed. Once again, you should always keep Nagashi Mangan in mind because it does happen. Some general advice I have is that the last row of discards is very dangerous since it is likely that players have reached tenpai at that point. If you are folding/bailing, then you should watch the discards closely and discard safe tiles. However as I painfully learned, keep an eye out for Nagashi.