GURPS MH1 Spells

===Anti-Aging Charms===
:AKA How to break the Masquerade and get rich
This is a spell that prevents the subject from aging during the duration. There's a couple of ways to look at it:
# Path of Body, Lesser Effect, Protect/Augment the Subject (3) aka Best Case
# Path of Body, Lesser Effect, Transform the Subject (8)
# Path of Body, Greater Effect, Protect/Augment the Subject (3) or Path of Crossroads, Greater Effect, Protect/Augment the Subject (3) 
# Path of Body, Greater Effect, Transform the Subject (8) aka Moderate Favorable Case
# Path of Crossroads, Greater Effect, Protect the Subject (3) & Path of Body, Lesser Effect, Protect/Augment the Subject (3) aka Moderate Unfavorable Case
# Path of Crossroads, Greater Effect, Protect the Subject (3) & Path of Body, Lesser Effect, Transform the Subject (8)
# Path of Crossroads, Greater Effect, Protect the Subject (3) & Path of Body, Greater Effect, Protect/Augment the Subject (3)
# Path of Crossroads, Greater Effect, Protect the Subject (3) & Path of Body, Greater Effect, Transform the Subject (8) aka Worst Case
# Path of Crossroads, Greater Effect, Transform the Subject (8) & Path of Body, Greater Effect, Transform the Subject (8) aka Supra-Worst Case
Basically, the GM needs to decide if non-aging is "subtle & localized" effect for path of the body, whether it is a protection/augmentation of the subject (ie, protection against the effects of aging, or augmenting youth) or a significant alteration (transform), and whether the ritual requires Path of Crossroads or not (and if it does, can it be cast without Path of Body). Targeting a being is definitely a greater effect for Path of Crossroads, and protection against aging is clearly protection.
There's also the question of whether this Alters a Trait, which make it cost additional energy. I'm going to say no to avoid doubling my paths.
The spell clearly has a duration and causes a physical change in the subject, so the energy cost for those needs to be added. We'll assume a 300 lb (or less) subject for 3 months, adding +16 energy to the cost.
We'll assume a slightly skilled witch with Magery 6 and Path skills of 16+ in all relevant paths, using a +6 Grimoire to make a charm with his Good Workspace Kit. He has FP14 if he needs to burn FP for some reason.
Throwing that all into a table, we get:
Case 	Greater Effects	Base Cost 	Final Cost	Estimated casting rolls
Best Case 	0 	3 + 16 	19 	0 (tap 2 sources and be done)
Moderate Favorable Case 	1 	8 + 16 	72 	4-5
Moderate Unfavorable Case	1 	3 + 3 + 16	66 	5-6
Worst Case 	2 	3 + 8 + 16	135 	9-10
Supra-Worst Case 	2 	8 + 8 + 16	160 	12
It's obvious that the moderate unfavorable case and the moderate unfavorable case are misnamed, but whatever.
In the best case, the witch can cast this from his energy reserve and some fatigue. Assuming no Breath Control, the witch can create a charm hourly with pretty much no complications - half that time is spent making the charm, the other half recovering the fatigue. Actually casting the spell takes 4 seconds (2x 1 second drawings, and then time doubling for using the grimoire).
In the moderate cases, the witch needs to generate 40-50 energy from ambient. With a +7 from gear bonuses on top of skill 16, this might be possible. Average rolls produce 13 + 13 + 13 + 12 + 12 = 60+ energy in 25 seconds with only a 10% chance of a failure (2.5% of critical) so this is reasonably likely.
In the worst case, the witch needs to generate 115 energy from ambient. That's something like 10 average rolls, taking the better part of a minute, but with a 20% chance of a quirk and a 3% chance of a critical. Since the critical effect averages 125 energy, which approximates an 8d directed attack on the caster... or instantly aging the caster around 18 months... this may not be too bad, but it's not entirely safe. The supra-worst case is just another 2 rolls, which is still pretty safe in this case.
;That's a hefty grimoire
Yeah, grimoires are cheap, though. But what it the witch has to cast the spell in the field without making a charm? The phrase completely screwed comes to mind. In all cases but the best case, the witch can't expect to generate much more than ~57 energy before the cumulative penalties get to high to draw any more energy, and even then about 1/4 of the last 4 rolls are going to be failures, quirking the spell wildly. Critical failure is a distressingly high 23% (for 12 casting rolls at or below skill 16)...
:Monte Carlo analysis of a skill 16 caster drawing 145 ambient energy requires 33 casting attempts, averaging 13 quirks, with a 43% chance of a critical failure blowing the caster to kingdom com.
Moral of the story is having effective path skills starting at 20+, and don't draw energy more than 9-12 times less the laws of repetitive averages catches up. Starting at a 20, 9 drawings average 81 energy, so that's not the end of the world by any means. 
;Talking to the Rev
See these forum posts to see how Jason Levine (MH author) interprets this stuff.
;TODO 
Write a program to figure out average safe energy, quirk level, and such for various skill levels.
:Program is written, needs to be cleaned up a bit.