There are several settings for スーパー牌 (suupaa pai - literally "super tiles"). There are green fives which are worth two Han plus two chips and gold sevens which are worth only one Han but three chips (and the chip value can be set at 2k, 5k or 10k points). These can be used in conjunction with up to six red fives (or red ones and nines) - and a host of other novel rules up to and including 青天井 (aotenjou - "skyrocketing") where the limits system is removed.
In this photo my neighbour has made an interesting (and valuable) set.
