Space mahjong
Space mahjong is a modified set of rules to mahjong originally conceived by the R18 game Itadaki jan-gari-anR. Here, the limitations on terminal tiles and honor tile are removed. Normally, the 1-9 scale ends with 1 and 9 as terminals. In this set of rules, the number sequence is given the wrap around effect when it comes to the formation of tile groupings. Another big difference in this ruleset is that you can call Chii from any player just like if you were calling Pon.
Tile groupings
Due to the wrap around effect, the terminal tiles operate just like any other numbered tile.
Numbered tiles
Honor tiles
With wrap-around effect, honor tiles become significantly important, for the fact that honor-related yakus are usually in high value, as well as they can now form mentsus efficiently.
Any three different tiles of kazehais / sangenpais can be formed as a valid shuntsu. That means all of the following sets are valid:
, 
, , , 
.
Any two different tiles of kazehais / sangenpais can be formed as a valid taatsu:
, ryanmen waiting for both 
and 
.- , kanchan waiting for both and .
, waiting for 
, can be interpreted as either kanchan or ryanmen.
Four different tiles of kazehais can be formed as a 4-sided tanki wait:
- , tanki waiting for .
Yakus
Tanyao
There's no more special combination generated by this ruleset. Everything works as still.
Chiitoitsu
This yaku is not allowed in this ruleset.
Chanta / Junchan
Aside from honor-tile shuntsus, there're two more available combinations of numbered-tile shuntsus: 891 and 912. This makes chanta and junchan become much easier than in regular rules.
Agari:
Honroutou
The restriction of Toitoi / Chiitoi-based hand no longer applies, as honors can be used for shuntsus.
The following hand shows how it is possible with Honroutou-nomi.
-
Agari:
Kokushi Musou
Opened kokushi is no longer unavailable since honor tiles can be grouped as shuntsus.
Agari:
Though the value of such opened hand is usually reduced for balancing purpose (e.g. 2 ~ 3 hans), since it makes kokushi musou significantly easier than menzen one.
Junsei Chuuren Poutou
Theoretically a 9-sided wait hand is no longer restricted to the regular form since numbered tiles can be wrapped around. That means such hand
Agari: (in regular rules)
can be interpreted as:
- Agari: (in space mahjong rules)
Though depending on rule details this may be recognized as a valid chuuren, or maybe not.