Chinitsu Challenge is a variation of Riichi mahjong. Besides having two players instead of four, the core differences are as follows:
- Only the 36 souzu tiles are used.
- Your starting score is 150000 instead of 25000.
- There is no dead wall or dora indicator.
- Calling chii, pon, and kan (other than ankan) are disallowed. The replacement draw on an ankan is drawn from the front of the wall.
- Riichi costs 0. There is no honba. There are no tenpai/noten payments.
- The game will allow you to chombo (e.g. by declaring Riichi when you aren't in riichi, or declaring a false win or a win while in furiten). This comes with a yakuman penalty.