Muto vim errata edit

[ExarKun]

My thoughts on that matter were already said.
Here:

MutoVim has to be cast on spells before they are created.

And something "before its creation" doesn't exist (you can't target Bismark with perdo corpus). So the target of MuVi is not a spell (it doesn't exist). It's magical energy, which ends when the spell is cast, after the effect of MuVi, and thus, the spell is perfectly natural.
The spell being not the target of the MuVi cast before its existence, but only the result of its application to its target (the magical energy worked in a spell during a process called "casting spell"), the MuVi :

• is momentary (however if your casting was ritual or ceremonial, it would have had a duration) in case of formulaic
• has to penetrate the penetration of the non cooperating caster (not the MR : magical energy is external), because penetration is the "strength" of a spell, and your spell has to force the other caster to affect his process of casting.

and here:

However I lack to understand how it can work since the Muto Vim spell resulted in a real consequence and I think this errata clearly create a paradox for muto vim magic.*
The "magical energy" you were working (which is not a spell) turned by your muto vim in a spell which is real; when the spell is cast, the "magical energy" is gone. So there is no more "muto" magic. This is enforced by the fact that you are only able to muto vim spell which are not yet cast. A spell not cast is not a spell, but magical energy in process of becoming a spell. PerdoVim can affect both. Muto is said to be imperfect regarding transforming magic.
So, IMO, it's like using a momentary muto spell to transform you in a geant form, breaking chains which were holding you. When the momentary spell is gone, the chains are still destroyed.

• the errata says that muto vim must have a duration for the spell affected, but muto vim says that it can't affect a spell. I think that thinking in term of "transforming the magical energy" is more accurate and answer the problems.

in summary:
1- muto vim CAN'T target a spell. Because the spell is "magical energy brought to existence" and MutoVim is not able to affect an existing spell. Otherwise, the limitation on "can't affect an existing spell" has no reason and is purely artificial.
2- thus Muto Vim is: "acting on the magical energy", the magical energy being the process by which a magus casts a spell
3- MutoVim only work on formulaic spell, because it is the process to alter the substance of the magical energy. Since spontaneous is already an alterance of magical energy, it can't be altered more (no sense to transform a human into the same human - magic wouldn't work).
4- The magical energy is always momentary: it appears only at the moment the spell is cast, briefly and immediatly produce a spell. For that reason, momentary MutoVim is the only legit duration for MutoVim.
(If you are ceremonially casting, the magical energy is only really used during the last round of your casting, which mean that all previous time is used to gather a bigger magical energy; it may even NOT be possible to alter a ceremonial casting formulaic spell because from one hand it requires a mystery "mercurian magic" which is innately opposite to MutoVim (which is a "spontaneous" approach of magic) and on the other hand ceremonial casting is borrowed from spontaneous type of spell casting; it may even not be possible to alter a ritual or it could require a duration for those particuliar cases: RAW don't say that rituals may be affected by MuVi and only adress formulaic.)
5- Thus, with a temporary MutoVim, you transform the magical energy of a formulaic into the magical energy of a spontaneous spell, but without most of the downside of spontaneous (which is the reduction of power, meaning the /2 or /5 to casting total) - depending on the guideline, Muto Vim is either a little side effect (guideline 1), almost an application of flexible formulaic magic (guideline 2) - except that MuVi can modify the base, which is something FFM can't - or a fully spontaneous spell (guideline 3 and 4 [4 being the addition of Creo requisite]) during a few seconds... the seconds which precede the natural transformation of that energy into a spell. The spell is thus perfect and not unnatural (as are the excrements of a magus turned into a dog).