[RPM] Low cost 'insurance' Luck for casters

[Terwin]

I was trying to determine what would be a reasonable construct for minimal cost 'Insurance' type Luck for an RPM caster.
The only purpose of the Luck is to avert critical failures relating to RPM(I think Gathering and Casting are the only 2 rolls where you get critical spell failures)

I was starting with:
Luck(Aspected Magic -20%, Critical failures while casting only -??%, Always on -??%, Self Only -?? )

I suppose my questions are, what should the value of Critical failures from casting only, is Always on a valid limitation, and what should it be worth.
Always on is supposed to reflect not having a choice as the luck will be used for any critical failure while casting, but I suspect that it would probably not be worth more than 5-10% if that, similar with Self Only.

I was looking at one or two levels of costs HP to further reduce the cost to -80%, especially if it makes Always On more valuable.(the character I am planning to purchase this with has all of 8 HP so even one point is a substantial hit)

I was also thinking Preparation Required might be a good fit, turning this into a sort of protective ritual that will automatically 'short-out' the next spell that tries to go haywire.

Note: RPM is not the only type of magic, but it is the only type of magic that this character has, there is another RPM spell caster in the party as well as someone who uses a different sort of magic.

Any thoughts?

[PK]

Some of your proposed limitations are redundant. For example, if you can only use Luck to fix critical failures, then by definition it only applies to your rolls. (Remember, the only time unmodified Luck can alter someone else's rolls is when you force them to reroll an attack roll made against you.) So what you really have here is the following. Note that "Critical Failures Only" is intentionally a very weak limitation because rerolling critical failures is the #1 use of Luck!

Luck (Accessibility, Only critical failures, -5%; Aspected, Magic, -20%; Nuisance Effect, Cannot choose whether to use it, -5%) [11]

[Nereidalbel]

Always On is not a valid limitation for luck, and only being useful for yourself isn't really worth anything on an Aspected Luck, either. To have it activate without thought from the character or player, that's Uncontrollable Trigger + Unconscious Only.

[Terwin]

It seemed kind of iffy, which is why I wanted to get opinions on it.

So looks like I'll need another -50% from Preparation required and Costs HP, and to check with the GM on whether he thinks it should have the Game Time enhancement.

Thanks.

[weby]

The criticals only would depend on your campaign, in my games the lost utility of not being able to use it on normal failures would be way more than -5%. As about half the uses of luck are for non critical failures when desperately trying to succeed in something, causing the pricing to be maybe -20% as accessibility. In PKs campaigns it is apparently about 10-20% that are other rolls.

For preparation require(a game time based modifier) you would likely need to have the game time modifier in place for it to make sense or you would be mixing game and real time.

A thing that I have allowed in my games for luck is "longer recharge time" where doubling the time to 2 hours is -10% and quadrupling to 4 hours is -20%. Most of the characters in my current campaign started with an unreliable, cost FP and 4 hour recharge time defensively aspected luck that they have since bought to full luck. (I do allow buying of a lot of abilities in game that many GMs do not)