Rule variations
Given the complexity to the rules of Japanese mahjong, the rules are even made more complicated by the existence of rule variations enforced among different groups and organizations.
Overview
The general rules of the game are complex enough. However, they are made even more complex, as various rules of the game can be toggled to different settings or simply by "on" or "off" (ari or nashi respectively).
Agari
A set of variations dictate how hands produce winning hands.
Agariyame
Allow the dealer to end the hanchan prematurely, while in possession of the lead in the round South 4 or in the West round after one hand has been played.
- Lead – Allow the dealer to end the hanchan prematurely, with the last dealer is in the lead.
- End – The dealer may end the game after one hand in the final round, regardless of point standing.
- Nashi – The game must continue until the seat winds rotate again.
Atozuke
Atozuke handles the rule for yakuless hands to gain yaku on discards. This is most common on hands waiting on more than two tiles, where one discarded tile produces yakuhai.
- Ari – Allow the hand to gain yaku on the winning tile.
- Nashi – Yaku must be embedded in the hand before the winning tile.
Double ron
Score two winning declarations at the same time.
- Ari – Discarder of the winning tile must pay both hands separately. Riichi sticks are collected by the first winner to the right. Some rules entitle the other winner to one of these riichi sticks if he has declared riichi during this hand.
- Check – Like ari, but the fourth player must reveal a non-winning hand, so that a triple ron can be avoided.
- Close – Atamahane, or head bump. Only the first win closest to the discarder is recognized.
- Far – Applying the head bump rule in reverse, where the player farther from the discarder overrides the closer player.
Furiten riichi
Allow players to declare riichi while they are furiten due to their own earlier discards.
- Ari – Allowed
- Nashi – Disallowed
Ryanhan shibari
Impose a two-han minimum at five or more honba (number of table counters). The two han must both come from yaku.
- Ari – Require two han from yaku at five or more honba.
- Nashi – One han from yaku is always enough.
Triple ron
Score three winning declarations at the same time.
- Ari – Discarder of the winning tile must pay all three hands separately. See double ron ari for distribution of riichi sticks.
- Atama – Atamahane, or head bump. Only the first win to the discarder's right is recognized.
- Abort – Do not score any hand, instead abort the hand with an abortive draw.
Chombo
Variations on chombo may involve its general usage. Common and casual games may not even enforce chombo due to the setting. On the other hand, high profile settings may require stricter enforcement and harsher point penalties.
Enforcement
Point deductions may be applied immediately after the incident, the hand, or factored after the game to avoid time delay during the game.
- Immediate – Chombo applied immediately.
- Hand – Deduction after the hand.
- Game – Deduction at the end of the game with raw points.
- Uma – Deduction applied after the calculation of the end game score.
- Null – Chombo disregarded.
Points
Point variation on the penalty points may be applied.
- Standard – The penalized must pay the equivalent of a mangan tsumo, just only in reverse.
- Mod – Modified amounts to the point penalty may be specified.
Toppling tiles
A penalty may be applied to toppling tiles of off the dead wall.
- Ld6c – If at least one tile from the dead wall is toppled, then the hand is declared dead. If six or more are toppled, then chombo is applied.
- Comp – This is a computer game. The rules infraction cannot occur.
Wall toppling
A penalty may be applied to toppling tiles of off the live wall.
- 6c – If six or more are toppled, then chombo is applied..
- Comp – This is a computer game. The rules infraction cannot occur.
Dora
Variations on dora involves a few implementations; and they all affect the number of dora used. The most common variation involves the akadora (red five) regarding its inclusion or exclusion. Other variations places options on the kandora and even the uradora. Lesser variations may include additional dorahyouji (dora indicators) at the beginning of each hand.
Furiten
If a non-riichi player ignores a winning tile, then temporary furiten is applied. Different rules apply as to when this status wears off.
- Turn – The player's next own discard ends temporary furiten. If the turn is skipped due to other players' pon calls, temporarily furiten is retained.
- Call – The players next own discard ends temporary furiten, but also any player's call of chii, pon, or kan, even for a concealed kantsu, ends temporary furiten.
Kuikae
This allows a player to call pon or chii on a tile, then afterwards discard the same tile, or a tile which would have completed the two revealed tiles at the other end of the sequence (switching chii).
- Full – Allow to discard any tile.
- Swap – Forbid discarding the same tile, allow switching chii.
- Nashi – Forbid discarding the same tile, forbid switching chii.
Kuitan
Allow the 1-han yaku tanyao (all simples) to be awarded to an open hand.
- Ari – Allowed
- Nashi – Not allowed
- Option – Tenhou.net offers both rules in different settings. One of the game rooms is set for both kuitan nashi snd akadora nashi. However, there is no setting for one or the other exclusively. The Korean rules write "concealed hand only selective", which sounds as if kuitan were an optional rule.
Naki
Variation may apply on tile calls. If several players call chii, pon, or ron on the same tile, this rule decides who will get the tile. Kan calls are treated like pon calls.
- Pon – Like pon above, but keep in mind that this is a computer game (C), not a ruleset for live play.
- Time – Pon trumps chii if called at the same time, otherwise the first call stands. Ron trumps anything, even if called slightly later.
Scoring
Scoring allows some flexibility to the rules regarding the start and end scores. Likewise, the oka and uma may be adjusted as well.
Tochuu ryuukyoku
Abort a hand and repeat it at the next honba (number of table counters) in case of nine terminals and honors, same wind discards, four riichi declarations, or four kantsu declarations. Some rules abort the hand upon a triple ron; that is not covered by this rule, instead see triple ron.
- Ari – Abort and reshuffle in these situations.
- Nashi – Do not recognize any of these abortive criteria. Play every hand until a winning declaration or exhaustive draw. Do not allow a fifth kan declaration nonetheless.
Yaku
Different yaku may be subject to rule variation. Some are simply not considered standard.