First time reading Ars Magica (5th edition), now that I'm finally at the spells chapter (not really sure why they put the Lab chapter between Magic and Spell) I've enjoyed seeing what the system is all about. When I came across the Muto Corpus section I was a bit confused though.
Arm of the Infant is level 20, and shrinks someone's arm to half its size. Its Base is 3 (Utterly change the appearance or size of a person) +2 Voice, +2 Sun, +1 Part.
But why would you do that when you can simply target Individual instead of Part? It'd be lower level, more effective at disabling enemies, and more utility, as you could shrink friends to sneak around or fit through tight areas.
Would Size modifiers come into play? It doesn't seem like it, as Arm of the Infant doesn't say anything about size, in fact, none of the MuCo spells do (transforming into a pig, a raven), and the Targets and Size sidebar only really specifies targets of the spell, not the result of the spell.
I feel like the power of Individual vs Part varies wildly on circumstance, and MuCo seems to handle Size strangely, as the Base 3 Guideline is very cheap for freely changing size with no limit. I'm just wondering if I'm thinking about this correctly or if I'm missing something.
If you want to shrink all of someone you have the spell Prenatural Growth and Shrinking just above Arm of the Infant Part is for when you want to affect only one part of the target.
I'd say that the spell Prenatural Growth and Shrinking is about the most you can change someone's size without extra magnitudes for the spell. There are some spells in other books that transform the target into a large animal that has +1 for Size.
Do check the errata for the Targets and Size sidebar, since it has some relevant additions.
I'd say that the spell Prenatural Growth and Shrinking is about the most you can change someone's size without extra magnitudes for the spell
Yeah that seems like a good baseline for simply changing size, and the Base 20 guideline that Cloak of Black Feathers uses probably factors in Size as well.
Choosing Part over Individual still seems like a waste though, not only in Arm of the Infant but Disguise of the New Visage
The target's facial features are transformed to any approximately human configuration you choose
Why not just target the entire individual instead of the face and save 5 points, gaining more versatility with the spell?
The target's facial features are transformed to any approximately human configuration you choose
Edit: Also Eyes of the Cat seems to do the opposite. It actually targets Individual, not Part (being the eyes). Though it uses the Base 2 guideline, "giving a person a minor ability," it still adds to my confusion on Part vs. Individual from the perspective of making my own spells.
It's an example of a part target. I've always taken it to be a prank curse. I much prefer the Arms of the baby T-Rex version of this spell.
As SG, if you use target individual in order to change a mere part, i would disallow it or add finesse and/or complexity penalties. HoH:S has some relevant guidelines and rules for finely detailed magical manipulations if images that could apply here.
Eyes of the Cat gives the ability to see like a cat. Anything happening to the eyes is cosmetic.
if you use target individual in order to change a mere part, i would disallow it or add finesse and/or complexity penalties.
That's fair and I'll probably use that, though my concern is not so much about preventing the abuse of using Individual to affect one part of the target, it's more the fact that Individual is just generally better because it's cheaper and affects the entirety of something. Though "generally" is important because it's all circumstantial, sometimes Part might be more powerful for some reason or another, but I feel Individual is better more often.
Think about this though. Arm of the infant will affect a giant whose arm is up to the max size for a +1 creature but individual target spells will fail if the humanoid is larger than size +1. Yes, you can add a size modifier when inventing or spontaneously casting but that also adds a magnitude so you don’t win out. There is a versatility to part that isn’t there with Individual.
In the ArM5 paradigm, affecting a part of a whole is more difficult than just a part. You can rationalize this easily considering partially modifying a human arm into an apparently sized crab arm, all of the necessary biological parts have to be changed and work together properly, whereas they do that naturally if you just change wholly into a human-sized crab.
Another viewpoint is that the whole is just one and changing one whole into another whole requires no further specification, whereas indicating a part of a whole to change into another part of a whole, just describing it, is already more complex.
I too noticed the oddity of Disguise of the New Visage apparently being a harder spell than a spell that reshaped someone's entire body. I feel like it was a fudge to make the spell come out at about the right level (not intended as a knock!). I think a spell to affect the entire body could maybe only do something simpler and less flexible? Definitely a YGMV area.