Some questions on Luck with modifiers.

[Boge]

I'm trying to come up with some original modifiers to Luck and some suggestions would be welcomed.

What would you consider the cost modifier to be for the following:

1. You get one reroll and choose between the two rolls.
2. You get one reroll and must take that roll.
3. Luck cannot be used on a critical failure or critical success from your opponent.

Can you use luck against another player doing something against you? Like you can make an NPC reroll on his attack roll. Can you do that to another player who is attacking you?

And using Luck on a reaction roll towards you, I guess you just tell the GM to roll and he chooses the best out of the three rolls?

[Kelly Pedersen]

Originally Posted by Boge

1. You get one reroll and choose between the two rolls.

I'd put that at -50%.

Originally Posted by Boge

2. You get one reroll and must take that roll.

-60%.

Originally Posted by Boge

3. Luck cannot be used on a critical failure or critical success from your opponent.

-10%

Originally Posted by Boge

Can you use luck against another player doing something against you? Like you can make an NPC reroll on his attack roll. Can you do that to another player who is attacking you?

You can use Luck to make someone reroll their attack against you, yes (see this post from Kromm for confirmation). In general, Luck can be used to reroll any effect that "affects you or your whole party". Attacks against you qualify (even if they're from another PC - I don't see anything that restricts that to NPCs), but something like a hacker rolling Computer Hacking to shut down your vehicle's controls while it was in motion would also qualify.

Originally Posted by Boge

And using Luck on a reaction roll towards you, I guess you just tell the GM to roll and he chooses the best out of the three rolls?

Yes. As per any roll (like damage rolls) where there's no target number as such, the person rolling will roll three times and you take the best result. Note that's the best result for you, the player with Luck, you get to choose. If you're trying to shoot a fleeing suspect, for example, and just want to cripple them, not kill, you could roll damage three times and take the lowest, if you wanted. You're not restricted to the highest roll mechanically.

[Boge]

The issue coming to mind is if I had the Active modifier, which requires me to use the luck before rolling at all, combined with the One reroll and have to take that roll, I suppose those two limitations can't be combined. Agree? It doesn't really work. Might as well just be the two die rolls to begin with, which is the -50% from what you suggest. Either way, I suppose they're both the max -80% cost.

And when I say can't be used on a critical failure or critical success from your opponent, I'm thinking that obviously you want to keep your own critical successes but not failures, and don't want your opponent to have critical successes but keep their failures. A HUGE benefit for Luck in the first place seems to be to save yourself from these situations. So, just 10%?

An Active Luck once per hour would only cost 3 points. Every half hour would cost 6 points. Every 10 minutes would cost 12 points. This would be declaring you're using Luck, roll two dice and take the best of the two. Do those costs seem fair?

[weby]

Originally Posted by Boge

1. You get one reroll and choose between the two rolls.

Originally Posted by Kelly Pedersen

I'd put that at -50%.

I would put it at mu h lower value due to the lower probability that the third roll impacts that much.

Below is the probability of success on a given target number with one, two and three rolls for the normal success ranges rounded to two digits after the dot.

target one roll two rolls three rolls
5       4.62%	 9.04%	 13.26%
6       9.25%	17.66%	 25.29%
7      16.20%	29.78%	 41.16%
8      25.92%	45.13%	 59.36%
9      37.50%	60.94%	 75.59%
10     50.00%	75.00%	 87.50%
11     62.50%	85.94%	 94.73%
12     74.07%	93.28%	 98.26%
13     83.79%	97.37%	 99.57%
14     90.74%	99.14%	 99.92%
15     95.37%	99.79%	 99.99%
16     98.14%	99.97%	100.00%

See how little the third roll actually impacts in most cases. The second roll is a huge help the third a lot less help. So I would make this modifier about -20%(using approximate accessibility modifiers) to -30% (more in line with normal GURPS modfiers as the general accessibility modifier seems lower than most other precalculated values)

So personally I would say -30%

Originally Posted by Boge

2. You get one reroll and must take that roll.

Originally Posted by Kelly Pedersen

-60%.

This is a bit more limiting mostly due to the thing where you would not want to use this in a "I succeeded, but would want to try for more success by", the raw probability of getting a critical failure instead of a failure after a failed roll on first roll is in most cases quite low. I would rate the extra effect -5% to -10%. So as the previosu was bit on high side I would make this total -35% maybe.

Originally Posted by Boge

3. Luck cannot be used on a critical failure or critical success from your opponent.

Originally Posted by Kelly Pedersen

-10%

I would rate it approximately the same.

Originally Posted by Boge

An Active Luck once per hour would only cost 3 points. Every half hour would cost 6 points. Every 10 minutes would cost 12 points. This would be declaring you're using Luck, roll two dice and take the best of the two. Do those costs seem fair?

I would make the total for such only -70%, thus: 5,9,18 points respectively. Due to the lower impact of third roll as described above.

[VariousRen]

Originally Posted by weby

I would put it at mu h lower value due to the lower probability that the third roll impacts that much.

Below is the probability of success on a given target number with one, two and three rolls for the normal success ranges rounded to two digits after the dot.

target one roll two rolls three rolls
5       4.62%	 9.04%	 13.26%
6       9.25%	17.66%	 25.29%
7      16.20%	29.78%	 41.16%
8      25.92%	45.13%	 59.36%
9      37.50%	60.94%	 75.59%
10     50.00%	75.00%	 87.50%
11     62.50%	85.94%	 94.73%
12     74.07%	93.28%	 98.26%
13     83.79%	97.37%	 99.57%
14     90.74%	99.14%	 99.92%
15     95.37%	99.79%	 99.99%
16     98.14%	99.97%	100.00%

See how little the third roll actually impacts in most cases. The second roll is a huge help the third a lot less help. So I would make this modifier about -20%(using approximate accessibility modifiers) to -30% (more in line with normal GURPS modfiers as the general accessibility modifier seems lower than most other precalculated values)

So personally I would say -30%

I don't have a strong opinion on if it should be -50% or -30%, but I think you're missing some subtlety in your data. You use Luck after you see what you've rolled - and you don't bother re-rolling a success. That means we're only interested in if the first or second reroll makes a difference, and your data shows that a second reroll can be major (at skill 10 it gives an extra 25% chance of success, at high skill it makes failure astronomically unlikely).

[kirbwarrior]

#3 should definitely be worth than -10%, that's largely why I and my players take luck is sniping crits. At least for the 15pts version, the other two make it safe to use it for other reasons. -30% might be a little high, but that's my gut first thought. A crit working against you sounds like something about hourly, so it's basically 15pts to be immune to crits (I might add that as a variant).

[vicky_molokh]

Originally Posted by Kelly Pedersen

-10%

IIRC Kromm said that Luck seems to be primarily kept in store to be used against nasty crits, so the limitation seems stingy.

[AlexanderHowl]

Luck is a very powerful ability, so I am hesitant to give generous modifiers, though I agree about the crits. I would rate them at -20%/-40%/-20% respectively, so a character that gets one reroll that they have to accept and cannot reroll crits could purchase Luck for 3/6/12. I would not allow the second modifier or the third modifier to be combined with Active because it does not make logical sense in the case of the second modifier and is a meaningless limitation in the case of the third modifier.

[Kelly Pedersen]

Originally Posted by kirbwarrior

#3 should definitely be worth than -10%, that's largely why I and my players take luck is sniping crits.

Originally Posted by vicky_molokh

IIRC Kromm said that Luck seems to be primarily kept in store to be used against nasty crits, so the limitation seems stingy.

While Kromm's group and others may primarily save Luck for crit-negation, I don't think that's universal. The groups I'm in certainly use Luck for re-rolling other stuff in combat. When you're shooting a weapon with RoF 10 and Rcl 1, for example, it's often worthwhile re-rolling a merely sub-average success, because every point of margin is one more that the opponent needs to Dodge.

Anyway, since Aspected (Combat) is worth -20% on Luck, I can't really see "not to cancel enemy crits" as being worth much more than that. Combat is really the only place in the rules where a critical success is an absolute "I just win" result - in most other things where an enemy crit is something that could be Lucked away, it's a Quick Contest of some sort, where you could use Luck to improve your own margin of success, and enemy critical success won't be absolute even if you don't. So, since "not to negate crits" is, in my view, not any more limiting than "Combat Only", and I still think it's less. I suppose I could go with -20% just for the neatness of the numbers, though.

[Boge]

weby, that table is wonderful. It was going through my mind yesterday, but I didn't want to try to figure out the figures. So that helps tremendously.

The suggestions are most welcome, guys. More are even more welcome. I might just take your suggestions along with my own and kind of average them. But it seems like my thinking is right along with you, so this might be easier to decide on than I thought.

Just as another suggestion, our GM says 50% for either (didn't ask about the critical one). I'm sort of leaning 30-40% myself. I don't think he'll have a fit if I'm cheating myself out of some character points. ;)