Perdo Vim Guidelines question

Hello everyone!
I’ve been reading through the Corebook, and a question came up regarding four Perdo Vim guidelines:

  • Reduce a target's Might Score by the level of the spell + 2 magnitudes, as long as the spell penetrates the creature's Magic Resistance.
  • Reduce a target's Might Pool by the level of the spell + 2 magnitudes, as long as the spell penetrates the creature's Magic Resistance.
  • Dispel Hermetic Form Resistance aligned to a given Form with a level less than or equal to the level of the Vim spell + 2 magnitudes + a stress die (no botch). Spell must penetrate the Vim-based Magic Resistance of the target.
  • Dispel Magic Resistance from a Might score aligned to one Realm with a level less than or equal to the level of the Vim spell + 4 magnitudes + a stress die (no botch). Spell must penetrate the Vim-based Magic Resistance of the target.

My questions are:

  • Why is there one guideline that reduces Might Score and another that reduces Might Pool?
  • Is the Might Score reduction from the first guideline permanent, or does it have a specific duration?
  • If the Might Score reduction from the first guideline is permanent, why would the other two guidelines (the third and fourth ones I posted) exist?

You might just want a creature to be unable to use its powers without killing it. Niche, I know, but it's an option.

More or less permanent, yes. I'm saying more or less because it isn't explicitly stated, and the realm book supplements also have ritual powers that reduce a creature's Might Score, and leave it to the troupe's interpretation the rate at which they get that Might Score back. Such that a troupe might decide to apply the principle to hermetic magic too, and consider that the Might Score can heal over time.

The third targets hermetic magi. The fourth - again - you might want to weaken a creature's resistance so that you can affect it with some low penetration spells without necessarily wanting to kill it or weaken it permanently.

I used both variant for different purpose. My magi has both a PeVi against Faerie at level 10 to reduce the might score, and a PeVi level 1 to reduce the might pool. I used the first one to weaken a fae, but if the fae remains belligerent, I use the other one to make her understand that I could do much worse (even if I don't have the PeVi 10 to reduce the might pool).

I also believe that there is somewhere a line saying that if completely strip from its might (permanently), there is no vis to be collected. Which would be a reason not to destroy permanently the might of a supernatural creature.

Can you tell me where I can find the part stating that if a creature's Might Score is reduced to zero, its Vis is also destroyed?

Also some beings are immune to having permanent Might Score reduction. See for example the "Immortal Magi" appendix of TMRE, the "Immortal and Unchanging" subsection on p.135:

Might damage, such as from Perdo Vim magics equivalent to Demon’s Eternal Oblivion, only results in temporary Might loss if the spirit is not utterly destroyed — full Might recovers by the next day.

"True immortals" are very different from things that "just have a Might score".

EDIT: I have also heard for years on this forum that might stripping permanently destroys the Vis, but I can't remember ever seeing a source (including looking back through old threads). Project Redcap mentions it in multiple places, but also never points to a source. Though Project Redcap also seems to think that might stripping below 0 can/will kill, which we know is clearly stated otherwise in multiple places through the line.

So until someone actually pulls up a source, I would take it as a "community leaning" that seems to be enforced by "I have heard this for decades so it must be true".

DE p.451 "An elemental that is reduced to a Might Pool of zero loses its animating force and becomes inanimate. In this state it can easily be mistaken for raw vis... If an elemental is damaged by destroying its matter — using Perdo (Form) or Perdo Vim spells, or water against a fire elemental, for example — then the vis is also destroyed."

I guess it is implied it also reduces the might score.

DE p.477 "As the demon's Infernal Might is reduced, subsequent Perdo Vim spells penetrate more easily, and have greater effect. The demon's body is actually eroded using these magics, and a demon that is reduced to an Infernal Might of zero is destroyed, leaving behind no corpse (and thus no vis)"

W