My character has a focus in trees. I am looking to make a spell that will shrink a tree so it is small enough to fit into my pocket. Any ideas on the base level to shrink a tree to the size of a mouse.
Relevant guidelines I could find.
From the book a +1 or -2 size change is a level 3 or 4 affect in the corpus and animal guidelines.
Changing a mouse to a plant (tree?) is a level 10.
Changing a human to a mouse is level 10 (level 20 for fish or small bird)
Any suggestions.
Assumptions :
Enlarging and shrinking spells always are hard to figure out but thanks to caribet, he provide us with a little something to easly calculate sizes and masses.
We can see it's easier to actually shrink than to grow (as seen in muto animal spells)
The base of the spell is then 4 to reduce 2 sizes.
Now we need to simply add one magnitude for each other two size decrement
Assume it's a touch spell and you want it to stay reduced for a sun duration
4 base, +1 touch, +2 sun +3 size
So it gives a spell lvl30 in muto herbam
Seems ok by me, hope it was usefull !
You left out the additional magnitudes to shrink the tree more than two sizes. I believe a big tree is +2 size from the basic size for herbam.
I was looking for something to change the tree to mouse size (-10).
Using your guidelines the base level to change a tree to a mouse would be base 35 (base 4 for -2 size, +7 for -14 extra size). So, tree to mouse sized tree,
base 35 touch +1, sun +2, size +2
level 60!
Yet, changing a tree to a mouse would probably be base 10
tree to mouse
base 10 touch +1, sum +2, size +2
level 35
It doesn't seem right to me that changing a tree to a mouse is so much easier than changing a tree to tree-sized mouse. Yeah ... the tree to mouse spell has an amimal req, but it still bugs me.
Well there really aren't guidelines for it.
In the first three editions there were no guidelines at all. All spell levels were chosen by looking at the established spells and saying, "well it looks a bit more involved than this one and a bit simpler than this one so I'll make it level 25". Which was, naturally, a pain for groups using troupe style play where different storyguides would rate things differently. This method did make sponting spells go much faster and I still use it fairly often when I storyguide.. "Put the book down, the spell you want is level fifteen because the storyguide says so, roll the dice and lets keep moving".
I suggest looking through the muto herbam spells and deciding what's easier and what's harder than your spell, and then back calculating the base level you want.
If it is level 35 to change a tree into a mouse, make your spell level 30. Don't concern yourself with the guidelines because first, there aren't any, and second, they're just guidelines.
Erik,
From a gaming standpoint:
Thats about the best damn (pardon me) answer I've ever seen.
But us players need numbers. 
An evil , bastard ST might shortchange us on spell effect otherwise. 
Looking at the Muto Animal and Corpus Guidelines/Spells, I think it is intended that any growth or shrinking that is covered by an objects "Individual" size is simply considered a Base Level 4 spell.
Witness: Growth of the Creeping Thing increases a -9 size "Thing" to 4x it's size, while Transformation of the Ravenous Beast To The Torpid Toad turns any animal (up to size +1, since its target is Individual) into a little toad (size -9).
I think your spell would in fact be:
(Base 4, +1 Touch, +2 Sun, +2 Size--only to effect such a big tree)= Level 25
From an abstract point of view, I think it should be easier to change a large tree to a seedling or even a nut than to a miniature version of itself. A very young tree is a natural object, a tiny mature tree isn't. Likewise a mouse is a natural thing, which offsets the added difficulty of changing plant to animal.
I definatly see what you're saying, but you could also say that this is the most unnatural thing of all, reversing the march of time.
I think this is one of those things that can go either way, like does being small make you better or worse in combat? Certainly the reduced reach would hurt a person, but then again, they are a smaller target, are below most shields, etc. A lot of these sort of things come up in trying to apply an abstract system to a concrete world.
I certainly agree that turning a tree into a nut is easier than turning it into a similar sized chunk of metal. I can't find any direct spell guideline for "de-aging" but aging (over the corse of a day)is a level 15 Creo Herbam (level 40 for a moment), one could argue that the reverse would be Perdo or Muto Herbam with a similar level, being the effect would be instant but only temporary. I could see "de-aging" being unnatural and adding a magnitude or two. Yah, I'm totally not digging this method.
Looking at Muto Animal, making a major change is a level 4, so we're back at the level of just transforming a Big Tree into a Little Tree. I wouldn't have a problem letting the designer choose if his spell did "Little Tree" or "Nut" (not both) for the same level. Then again there's only one guideline under Muto Herbam "Level 3: Change a plant". So maybe any change from living plant to living plant (including nut) is level 3...weed to mighty oak.
If I was your Storyguide and you had a really passionate belief that it should be easier to do "Nut" than "Little Tree" I wouldn't have a problem putting another magnitude on "Little Tree".