A character attacks a monster. The character rolls their attack roll first. The monster rolls second, but the combat is simultaneous. If the attacker loses the combat roll can he chose to reroll any number of the attackers dice after the combat is complete or does the attacker need to reroll immediately following his attack roll not knowing whether it is needed (as it depends on the simultaneous defense roll)? Consider that the lucky stone is a one use item then discarded. Counter argument of the defender is that the attacker roll happens first and cannot be rerolled after the defender rolls. Only the defender with a lucky stone gets the benefit of the item? Seems wrong to me as the item is a very powerful one use item.
The rulebook is not clear on if combat is simultaneous, or if the attacker rolls before the defender. The only thing is says is:
When you make an attack, roll a number of dice equal to your Might. Your opponent does the same.
Normally, it makes no difference, but with the Lucky Stone; you must decide if you want combat to be simultaneous or not. There are many little rules like this in Betrayal where your group needs to decide which way to play it. Either way, the Lucky Stone can be used, but your knowledge would be different in each case.
The Lucky Stone is used "after you attempt a roll of any kind". It is reasonable to assume this means "immediately after", or before anything else has happened. Therefore, there are 2 options:
If you play with simultaneous attacks, then the player with the Lucky Stone can choose if they want to use the Lucky Stone after the players have rolled their dice. The player will know how the defender rolled before making that choice.
If you play where the attacker rolls first, and then the defender rolls, then the attack should have to decide to use the Lucky Stone after rolling, before they can know what the defender will roll.
In the second case, the Lucky Stone is still useful, but using it might be a risk as the defender could end up rolling really poorly so that they didn't end up needing to have used it.