Virgilio Hohlfeld:
Say, it just occurred to me -- Luck with a pretty tight limitation should be a fairly inexpensive advantage. It's 15 cp when applicable to any roll, once per table hour (a time frame that still isn't well defined at our "table"). If it were applicable only in narrowly limited circumstances, say against critical spell failures, it seems like it might be as little as 5 cp.
That's not a good Advantage Build considering there are canonical methods that are more expensive:
Magery Enhancement: Stable Casting +40%
Whenever you roll a critical failure with a spell, you can try to “stabilize” the magic by making an immediate second roll against the spell skill, without range penalties but with all other applicable modifiers. Success turns the result into a normal failure.
This cannot be combined with the Radically Unstable Magery limitation (p. 26).
There is also a Perk, which is cheaper, but may end up more expensive than "5 points" overall:
Stabilizing Skill: You can use a particular mundane skill – set by the GM – to avert critical failures with the spells
of one college, as per Skills to Salvage Critical Failures (Thaumatology, p. 40). Specialties must name both skill and college; e.g., Stabilizing Skill (Meteorology for Weather spells). See Elemental Styles (pp. 4-5) for skills suited to each college. Mages who suffer from Radically Unstable Magery (Thaumatology, p. 26) cannot have this perk.
Prerequisite: Relevant skill at 15+.
-- Note, no matter how high your Stabilizing Skill is, it counts as maximum 15 for stabilization purposes. --
Technically, you don't suffer from "Radically Unstable Magery" so you can go those routes...
technically...
And lastly, any Luck build for averting Magical Critical Failures should be Luck [9] (Critical Failure Only, -30%; College Specific, -10%) or maybe Luck [5] (Critical Failure Only, -30%; Spell Specific, -40%)... or even maybe Luck [10] (Critical Failure Only, -30%). Further limiting it to only "Critical Spell Failure" should only be another -10% or -20%, because when you look at the Character, where is it going to most apply? Critical Skill Failure in combat? No, you'd probably hold it for your spell casting, so it's not going to be really useful to
you aside from avert spell catastrophes. And yes, that has to be taken into consideration when building custom Advantages and Disadvantages. And as a GM I'd hesitate to allow that last build, especially on a character built with
Mana Enhancer, as that drawback is why Mana Enhancer isn't a
lot more expensive.
Why is "Critical Failure Only" at -30%? Because it's really only limiting the Advantage at worst by 80%, but in practice, by about 50-60%. "19%-31% effective" as an Accessibility Limitation is -30%. I'd even look at knocking that down to -20%, but GURPS has a bit of "pentaphilia" built into it, and Luck (Critical Failures Only) at 10 "feels" better than it being at 12, so I'd only adjust the Limitation down to -20 or -15% if I were tacking something extra on, like "Costs FP -5%/lvl" (and mostly just to get it to round to 10).
Also Daredevil is a "Critical Failures Only" Luck+Higher Purpose rebuild, Daredevil [15] (Luck [10] (15; Critical Failures Only, -30%), Higher Purpose [5] (Daredevil Behavior))... so, Critical Failures Only at 10 points is kinda canonical (if you squint at it).
But honestly, 'Luck Build" isn't the direction I'd go as a GM, I'd aim the Player at Perks as 1) it's a canon build and option, 2) Perks have a limiter, and 3) Perks are how a number of other characters have been handle so far in the game... (and as a GM I've really taken a shine to using Perks to resolve "low cost Advantages" rather than overly complicated builds trying to eke out every last Limitation...)
Why am I not lining "College Specific" up with "One College Only" and "Spell Specific" with "One Skill"? Because One College Only is exclusionary, you can never buy another version of an Advantage with One College Only, however the lowest value of "Limited Colleges" is -10%. Similarly, One Skill Only was priced at altering
a combat Advantage*, so the necessary skill listing is rather short, however the list of possible spells is quite large, so it deserves a boost.
When weighting Enhancements and Limitations in GURPS is a bit holistic, you can't just look at percentages in a vacuum, some were designed with very focused utility in mind, and that has to be taken into account.
* Yes, I know it's started cropping up everywhere, but if you look at the Advantage and the list of possible skills that Advantage could apply to when it's somewhere other than "Extra Attack", the list of skills tends to be rather constrained.
