I never really used it (mainly, I think) because I never really understood it. I tried it once or twice on small stakes but I guess I never looked closely at the rules or something. I'm not saying I'm typical in this, I'm just saying it's what my experience was.
No rules on this, if you roll higher than your opponent than you win, it is just as simple like that . So you will enter whatever secret lucky seed to help you win but if luck doesnt shine upon you, you will keep on rolling lower than your opponent
