In terms of gameplay, Mahjong Competition Rules (MCR) is generally similar to other most varieties of mahjong, in that it uses all three usual suits (bamboos, characters and dots; respectively 索万筒 in Chinese), and the honours tiles consisting of the wind tiles (风牌) and the dragon tiles (三元牌, also known as 箭牌), as well as the usual eight flower tiles, although the flower tiles are less important in MCR compared to some other variants. The main differences between MCR and other variants lie in the scoring and some rules.
Points are calculated using simple addition
Winning hands in MCR are scored in points, where various patterns or score elements achieved are awarded different amounts of points and added up together in a simple sum. In most mahjong variants, particularly more traditional variants (Singapore Style, Chinese Classical, Hong Kong Old Style, Japanese etc.), winning hands are calculated based on doubles or fan (番) achieved. Base points are calculated, then doubled for each doubles scored. Hence, if a winning hand earns five doubles, the base points are multiplied 32 times (i.e. base × 2 × 2 × 2 × 2 × 2). Basically, points calculated using doubles increase in a geometric progression, compared to MCR's arithmetric progression, which is much simpler to perform. But this does not mean that high-scoring hands are not possible. They still are; difficult-to-do hands like Thirteen Orphans (十三幺, sometimes better known as the Thirteen Wonders) are inherently worth more points.
8-point mininum in order to win
The conditions for making a winning hand are rather different in MCR. Technically, in most traditional variants of mahjong, as long as the hand has four completed sets of three (either as sequences or groups of idential tiles) and a matching pair, it can win. However, several variants have implemented some minimum requirement for a win. For example, in Singapore Style mahjong, most players prefer to have a one-double minimum. In Hong Kong Old Style (HKOS), some people have a 3-fan minimum.
In MCR, the minimum number of points that would allow a player to hu (胡), to win, is 8 points, which is calculated from a variety of score elements. In MCR, there are 81 patterns/score elements (called fan 番, but without the meaning of doubling here) each with a point value ranging from 1 to 88. This may seem like a lot for the beginner to learn, but many of these are related to each other, so it is not a hopeless task!
Each game has only 16 hands
In MCR, the dealer does not remain dealer even if he wins or if there is a draw. The dealership passes on to the next player. Thus, a full game of four rounds has only 16 hands.
Since scores are tabulated after each game, and scores are not carried over to the next game , players have to think strategically throughout the game to try to earn enough points (relative to each other) in order to obtain a good position. In competitions, table points are awarded to each player at a table: the player with the most points get 4 table points, the player in second place gets 2 table points, the third-placed gets 1 table point, and the last player gets 0.
Flower tiles do not count towards the 8-point minimum
Flowers in MCR are special bonus tiles. For the 8-point minimum required to win, flower tiles are not counted. Instead, flowers are treated as bonus tiles, which contribute one point each after the 8-point minimum is reached. This is meant to reduce the effect of luck.
In addition, flower tiles can be discarded when the going gets tough. In dangerous situations, freshly drawn flowers may be discarded as a safe discard (no one is able to win off a flower!), instead of having to get a replacement tile which may be a tile that some player is waiting for in order to win with a high-scoring hand.
Discards are lined up in an orderly manner
Unlike in Singapore Style and HKOS mahjong, where tiles are haphazardly discarded in the centre of the table, discards in MCR are made orderly. Each player will line up his discards in rows of six, such that everyone can see clearly all the tiles and the order in which they were discarded. This increases the analytical element of mahjong, where players can play defensively by reading the discards of opponents and taking precautions in discarding dangerous tiles.
No tile discard is sacred!
Actually, this refers to the Sacred Discard rules in Japanese mahjong, where players are not allowed to win on tiles they had previously discarded and other details pertaining to discards. In Singapore Style and other similar variants, there are rules that prohibit players from making actions pertaining to fresh discards within one turn, or illegal chows. In MCR, such actions are actually permitted.
In MCR, players have more freedom to chow, pung and win on tiles. A player can discard a tile, then make a pung or win on the exact same tile discarded immediately by the next player! Of course, one would wonder why a player would do that in the first place, but this is evidence of the subtleties of gameplay that can occur in MCR. For example, the player who wins on the tile he just discarded could be trying to win off a particular opponent. Or he may not have enough points (i.e. the 8-point minimum) to win unless he wins off an opponent's discard (a few situations are possible: winning hands that require Last Tile, Melded Hand, Last Tile Claim).
There is no Dead Wall
The Dead Wall refers to the stack of tiles that are not used towards the end of a hand. For example, Singapore Style mahjong typically keeps 15 tiles in the Dead Wall, while most other variants have a Dead Wall of 14 tiles. In MCR, all tiles are used, so players have a chance to win right up to the last tile. If no one wins off the last discard, the hand ends in a draw.
The player to draw the very last tile has to discard a tile too, unless the player can make a Kong, which then leads to a situation where he is supposed to draw a replacement tile, which is not possible since there are no more tiles left to draw upon. It would seem logical that he cannot make both a Kong, not draw a replacement tile and still discard a tile. So, in such a case, discarding a tile is not necessary. In the case of drawing a flower, a player can also display the flower in order to draw a replacement tile (of which is not possible, a situation identical to that of a Kong, as mentioned earlier). However, it would be much easier to just discard this flower, since it is always a safe discard!
So, these are the bare bones of the Mahjong Competition Rules! These rules are rather different from the other variants, are they not? There are some more things to talk about, such as how scores are calculated, but I will leave those for another post.