Generation of the Luck stat would be a straight 3d6 roll. Whatever you get, you're stuck with. Obviously if that doesn't work, you can change it.
A player may substitute Luck for any other stat when making a check. The player may decide to substitute a Luck roll, even if they have orginally failed the inital check. When Luck is used however, the result stands even if the Luck result is worse than the inital roll.
The number of times that Luck may be used in a game session is determined by their attribute bonus. A character with a Luck of 13-15 would therefore be able to use their Luck once per game session.
A couple of bits that would be much more dependent on the individual DM and the type of campaign they're running:
What to do with an "average" luck? My personal inclination would be to allow them a single Luck roll too. So a Luck stat ranging from 9-15 would result in a single roll each game session.
What do you do with a negative stat? Depends on the DM really. I personally would allow the player to pick a roll sometime during the session where the substitution of Luck could result in Dramatic failure (a failure that works within the story) but doesn't/won't result in the actual death of the character.
An alternative would be to simply only allow one Luck roll as normal, but the negative modifier on the attribute is applied to the roll.
A third alternative would be to say that you get one roll as normal, and that Luck checks with a positive attribute can act as if they were a Prime, and negative modifiers means it's non-Prime.
Obviously the options could be mixed and matched around to suit the feel that a DM wants. The main point for having something like a Luck stat would be to introduce an easy to keep track of method for Drama Points/Action points, as well as being a quick and dirty stat the DM can check against for those odd situations that come up.
Feedback, suggestions?
