I'm planning on running a story that will have several magical creatures, but I'm a bit fuzzy on how magical might works to power spells/effects
As I understand it, MM works like this: A BushyHeadedSnickdoodel has a MM of 50, it can levitate at a cost of 10..... does this mean it can do this 5 times, and then its might is used up and it dies? I feel I'm missing something, any help would be appreciated.
-Ag
No book here right now so this is only from my memory.
A creature has a magic might and it has might points. Might points are used to power effects and they regenerate (I think that default critters can get a full recharage after a day). Critters have a maximum number of might points equal to their magic might.
Magic (infernal/holy/faerie) might is used for summoning the critter, warding against the critter and the critter's magic resistance.
Spells like Demon's Eternal Oblivion destroy might not might points.
A critter that uses all of its might points is still doing ok it just can't power any more effects.
If a magical creature has an effect that targets a magus does parma or any other resistance come into play?
If it does, is there anyway to increase penetration?
eg: my BushyHeadedSnickdoodel can make yer hair turn green fer 2 of it's 50mm points. (say a lvl 5 mutocorpus like effect). How would a magus with a parma of 2 and 9 in all arts treat this?
-his hair turns green. no resistance?
-effect has no "built in" penetration, he's fine?
-effect doesn't exceed his corpus resistance, he's fine?
Would the following be valid?
The BushyHeadedSnickdoodel sees that your hair is still normal he uses 10mm points to give an effective "casting score" of 25 for a "5th level" spell giving a penetration of 20, the Magus' hair turns green.
There is nothing clear on the matter. Different 4ed supplements dealt with the matter in different ways.
We know that before parma, there were no general MR available save from actual Might but MR did exist.
From this I would extrapole that creatures should have a way to boost their penetration.
given that the base penetration value is 0
Option 1: Creature penetration total is Might pool - Spell level/5
Option 2: Creature can boost penetration at the rate of one might point for two level of penetration (same as magical obj or vis)
Option 3: Creature does not have a penetration value
I can see any combinations of these 3 options be applied to a given creature. There should not be a general rule since creatures are always unique in some way.
Ex. BushyHeadedSnickdoodel can make yer hair turn green fer 2 of it's 50mm points (lvl 5 mutocorpus)
Penetration:
Option 1: 49
Option 2: [0;96]
Option 3: 0
Option 1+2: [49;145]
Note that @ 50 might point, your BushyHeadedSnickdoodel is more of a GodLike BushyHeadedSnickdoodel
Hope it helps,
W
Fifth Ed. on the other hand is completly unabiguous on the matter. The details are in the front of the Bestiary(?) chapter in the rule book.
The penetration of an effect is equal to the creature's magical might minus the number of might points required to power the effect. You'd be wise to double check rather then trust my memory.
If my memory is correct, in your example the green hair power has a penetration of 48 and your magus has a resistance of 19. The magus will have green hair.
Ah. hmmm. Nice
W
there may be a way to boost penetration by putting in extra might but I haven't looked over this section of the rules in months. I'm not at all sure I provided the correct information.
Your memory is nearly correct. The section you recall is the Magic Resistance and Penetration chapter of the Creatures of a Realm section, ArM5 p.184.
Only that you subtract 5 times the point cost from the Might, then add an eventual Penetration bonus from Penetration skill of the creature, to get its final Penetration. Which in the example hence is a still whopping 40.
And now back to the ever popular question: do BushyHeadedSnickDoodles dream of the Pink Dot Defense. 
Kind regards,
Berengar
Salvete Sodales!
5th edition rules are clear but differ slightly from the system described above:
(page 191):
CREATURE POWER PENETRATION: Might Score - (5 x Might Point cost of the power) + Penetration Bonus
In your example the green hair would have a penetration of 40 unless the creature has the Penetration Ability (works in the same way as for a magus) - still too much for your magus' MR.
Vale,
Alexios ex Miscellanea (aka Lars Gerlach)
P.S.: Sorry, I was too slow and can't eleminate this post, so ignore it.