Appearantly I'm stupid, because I don't understand the wizard's boost.
Does it increase the effective level of the modified spell?
How drastically can it change another spell? - or is it more of a "ordinarily I would be able to affect only dirt with this terram spell, but now I boost it to affect stone"?
IIRC the spell says that "the storyguide determines how the boost affects the spell", so it is whatever you want. You are not stupid: this spell has never been used in my group because nobody figured out exactly how to use it. If it affected penetration of the original spell, if the effect on a given spell was regular or not (if you always increased the damage of the Pilum of fire or affected the area it covered, for example, and if it changed between castings) and in general found it more confusing than anything. Been there since we are aware of it, though.
Not a very clear answer, just to clarify that you are not alone in your doubts 
Cheers,
Xavi
I would say this have to be discussed with the SG.
Since it boosts the "power" of the affected spell by 5 levels, I would say this:
- Penetration - No effect. The description says "power", not level. In fact, if it increased the "level" of the spell, it probably would REDUCE penetration. And you have Wizard's Communion that can be used to increase penetration, so that is covered by another spell.
- Range, Duration, Target - no effect. Stated in the spell description.
- What it would do - Look at the base effects under the spell guidelines. The spell that is being boosted will, for example, (CrAq 15) Creates a poison that causes a Heavy Wound. The boosted version would create a poison that causes an Incapacitating Wound. This is all straightforward.
Where the SG comes into play is when the base spell has an effect that the addition of 5 levels would be hard to figure out. Sticking with CrAq, look at Mighty Torrent of Water. +10 damage plus a potential knockback. What happens when this is boosted? Since the guildlines have nothing, we need to look at the boosted spell. Does it do more damage? Is the knockback harder(impossible) to resist? Is it a combination of both? What we do know is that it won't effect more than one target (different Wizard's Boost spell). If I was the SG, I would go with whatever the play is looking to do. More damage or better knockback.
As an aside, I can see where Wizard's Boost (Co) could be very useful to bump a healing spell up a level to temporarily cure an Incapacitating Wound so the player/npc can get back to the covenant for real healing. Tough to drag those unconscious players around on the back of a horse and bad for their health too.
Edit: Also useful if you can penetrate the target but do no damage due to soak. The boosted spell may allow you to damage them!!
No, you are not stupid (or at least not because of this particular oddity...). My troupe doesn't use this spell as it seems to be a cheat and doesn't really fit within the framework of the rest of the rules. In other words, it sort of sticks out. I think it was originally included because there were so few CrVi spells, but I could be mistaken. I'd ignore it.
Perhaps a remnant of olden days. Who knows what ideas the original authors may have had with it.
To me, it sounds like a spell to use mainly for pumping up combat spells - like +5 more damage from the CrIg spell, or boosting the PeCo from a light to a medium wound.
Other spells like Wizard's Reach, can boost the Range of a spell one magnitude. I imagine there could be similar versions for Target and Duration as well. In this case, I'd say that the effective magnitude of spell is raised, so Penetration drops. Otherwise it seems too good. Dure, I know you need to have a Vim spell to cast alongside the primary one, but you get a lot of flexibility. And the virtue Flexible Formulaic Magic does it this way.
Edit: Wizard's Boost for a healing spell...surely either the healing spell needs to be raised one effective magnitude - since you heal a larger wound suddenly - or else the Boost on a Ritual spell needs to be a Ritual as well. Otherwise, too good IMHO. Sure, I know you still need to whip out a high magnitude Vim spell to do this, but...
So, you think that it would be a 1-parameter only (or effect, in this case) bump to the spell using Flexible Formulaics as a benchmark? It is a way of seeing it, certainly.
Cheers,
Xavi
I'd say you can only bump each parameter once, per spell. So casting Wizard's Boost, Wizard's Reach, Wizard's Time and Wizard's Effect can bump the effect by one magnitude as well as Range, Duration and Target. And even combine to with FFM.
Exempli Gratia: Consider the spell "Shear the Sheep" PeAn5 Vo/Mom/Ind, which "does superficial damage" like removing the hair of an animal.
Wizard's Boost => "Pain but no real damage".
Wizard's Reach => Sight,
Wizard's Time => Concentration
Wizard's Effect => Part (that's no use, but combine with FFM => Group)
Suddenly you don't remove the hairs on an amimal within shouting distance. You cause ongoing pain to a group of animals as far away as you can see them. This would be a PeAn30 in its own right. But you still have to cast 4 additional Vim spells. And you need FFM as your Major Hermetic Virtue. Sure, it's flexible, but expensive (in time and virtues) and difficult.
The Vim spells don't alter the effective level of the spell, it's still only a lvl 5 - but FFM pumps it up to 10. So penetration is as for a lvl 10, not a 30!
Is this the trade off? Do you get better penetration this way, by doing all this extra effort?
Or can you only alter one single parameter on each spell?
Of course MuVI doesn't increase the level of the spell... it's all the point of these spells: casting "big" spells with "big" penetration, without a wizard's ceremony of communion casting!!
If i have a 20 peco spell at voice, with 50 penetration, i could go with a MuVi to go to SIGHT but still with 50 penetration.
If my 2d friend cast also wizard boost to a heavy, then it's a "30" spell.
And most: you keep masteries for your 20 PeCo... casting a effective 30 PeCo you haven't.
Muto Vim is powerful, but you need to be ready.
Which is precisely why I believe it's a sort of "cheat", a way of doing an end run around the spell level subtraction from Penetration. You get a 30th level spell for the price of a 20. Seems like everyone should do this all the time, but then it makes the spellcasting rules even more complex.
As a sidenote, it was used in earlier editions mainly to boost a spontaneous spell, giving your 5th level "create a bucket of water" enough extra juice to to fill a barrel. I don't recall it being applicable to formulaic spells (making your +30 BoAF a +35), but I could be wrong.
Ok, I don't remember any of that. But I can't claim to have researched it much either. Which Edition?
Ok, 4th ed Wizard's Boost needs separate spells for each of the 10 Forms - so it's Wizard's Boost [Form]. It also needs to specify whether it affects the "power", range, duration or target. In effect, there are 40 different versions of this spell. There is no mention about allowing - nor disallowing - it to affect Spontaneous magic. It says "A Wizard's Boost may never affect a single spell more than once", but this is still a bit vague as to whether only one WB at all can affect, or just one for each of Power, Range, Duration and Target. I'd say the former - just one single WB spell - not all those. Because of this, I can live with the effective spell level not being raised, since this only means +5 Penetration.
I wouls say precisely the later: you cannot keep casting range enhancement spells to make your Touch spell an Arcane Connection spell, but you can boost both range and target without problems. Still, you need so many fast casts that you are bound to botch there.
On the other hand it is a great spell (or combo of spells) to have in your Talisman, now that I think about it.
Cheers,
Xavi
If that is the exact quote then i dont think there is any room for interpretation as it specifically says a single SPELL more than once. Not spell variable or similar.
That is the exact quote - from 4th ed mind you! IDHMBWM, but I have the 4th ed pdf.
And I agree, is says spell not spell variable. I completely support the fact that one variable cannot be boosted more than one magnitude.
However...the term "Wizard's Boost" can refer to one of the four possible spells (power, range, duration and target). So nothing per se says you can't cast all four different ones on the same target spell. Personally, I'd say it can be abusive to allow this. So I'd allow only one variable to be altered. But this is an interpretation, open to debate.
And on a (somewhat) related note: Can this only be used to boost a spell? I mean, it's Muto, not Creo. What if I wanted to go down a magnitude, in one variable? Say a Sight Spell where Voice is enough? But why would I, if the magnitude of the spell doesn't change? If it doesn't for boosting, it shouldn't for minimizing either. But it could be useful where some R/D/Ts have several option for the same magnitude...Eye and Touch are the same Range, right? And Duration: Concentration and Diameter? This spell ought to be able to change it like that as well. Wizard's Range can change Range up or down one magnitude, or change the parameter within the same magnitude as well, and so on.
IMO Wizard Boost is just an all-encompassing spell because they did not want to write 50 wspells in the MuVi section of the book. The 50 spells are 50 different spells. The statement is only there to prevent you boosting (with the same EXACT spell a touch range spell into a Sight range rspell or a candle fire into a BOAF. You can still use several spells of the "wizard boost" pack to boost a spell a magnitude in size and another magnitude in range, for example. Niothing wrong there.
Cheers,
Xavi