I've already posted this question on the David Chart Ars Magica 5th edition mailing list, but I figured I would cover my bases to get the broadest range of replies.

Page 191 describes the Might Score and Might Pool of creatures.

Some spells, like Demon's Eternal Oblivion (pg 160) and Lay To Rest the Haunting Spirit (pg 150) describe that they deplete the target's Might if they penetrate the target's Magic resistance.

Is this a reference to the target's Might Pool or Might Score?

Assume a Demon of Might Score of 15 and a Might Pool of 12.

A magus casts a level 10 Demon's Eternal Oblivion spell with a Casting Total of 28 and Penetration Ability of 0.

Penetration of (28-10 = 18) beats the demon's Might Score of 15, so it affects him.

What happens?

A. Does it reduce the demon's Might Score by 10, bring it to 5, and making him easier to affect in the future by lowering his Magic Resistance? If so, should I assume the Might Pool is capped by the Might Score and thus also reduced to 5?

OR

B. Does it reduce his Might Pool by 10, depleting it to 2, and simply reduce his ability to use his powers?

If the result is option A, is there any way for the demon to recover his Might Score?

If the result is option B, how can the demon ever be destroyed as described by the spell? If its Might Pool is reduced to 0, it can't use any powers, but is it further impeded or affected?

Thanks ahead of time for helping address my ignorance on this matter.

"If the result is option B, how can the demon ever be destroyed as described by the spell? If its Might Pool is reduced to 0, it can't use any powers, but is it further impeded or affected?"

You answered your own question. When a creature's Might Score equals zero, it's destroyed. When the Might Pool reaches zero, it can't use any nifty spell-like effects. A demon could still gore, impale, crush, etc... you with a Might Pool of zero. A demon with a Might Score of zero, is just a smoking pile of brimstone and ash, and maybe a little tainted vis.

However, that still hasn't answered my original question. Does the spell affect the target's Might Score or the target's Might Pool?

Which one?

//Sorry, the Might Pool and Might Score are both reduced by the spell level, if it penetrates.//

Hmmmm... interesting. I'm not saying you're wrong, but that's not how I would think of it.

I don't claim to have the expert knowledge and intimate relation to the thinking the Game Designers that my fellow schmuck Berengar claims to have, but let me run my thoughts past you forum-ites.

It was my impression that the clarification between Might Score and Might Pool was made to fix the Death-Spiral that was the doom of anything with a Might in previous editions. As a Demon/Fairy/Dragon used its spiffy powers, it's Might was depleted, thus reducing its Magic Resistance and making it easier to defeat.

By making the Might Score a constant, and pitting your Penetration against that, then a Creature is allowed to used its spell-like abilities (powered by points from the Might Pool) without making it sexily vulnerable to Penetration.

For Faeries and Dragons and Werebears (oh my) the complete depletion of the Might Pool would be an inconvenience, but they are tied to Mythic Europe, and thus would remain. A Demon/Devil, however, is a creature of another realm entirely... so the depletion of it's Might Pool sends it back to where it came from. This is a weakness of Demon Kind that the Order has learned to exploit, via spells such as Demon's Eternal Oblivion.

Even better, however, is zapping faeries with a variation of Demon's Eternal Oblivion that I came up with for my last Magus... I call it "Gift of the Mundane" and it's great for swatting annoying Fey (i.e.: "all of them"). They don't disappear, but it's fun whacking them with a Medieval Flyswatter when you deplete their Might Pool.
;-)

This is just my interpretation, flawed though it may be by my not being a "Mighty Playtester O'Power"... but it's the one I've used since I started playing this game.

Hell, they may have fixed that Death-Spiral thing themselves in 4th ed, but we pretty much only crack the book when we have new players or to argue spell guidelines.

J.