I really, really think we need something like this, especially given how this can be tricky.
And I'll inaugurate things with my own spell idea to submit
There's this possibility that, in the future, Hiems would want to invent a spell to freeze people up, to immobilize them without killing them or endangering them in any way.
By RAW, this is pretty simple: ReCo, with the "freezing" being cosmetic only (which is made easier by Hiems sigil).
But, the problem is, I think this kind of spell is perfectly appropriate for him, and would like it to fall under his focus, because of this. But I don't think a simple cosmetic effect would allow this (I'd disallow it as a GM)
So, my question is: If I add Perdo and Ignem free requisites (no +1 mag because it doesn't enhance the effect, like damaging people), would you feel this'd be okay or not?
Balance-wise, it'd be more powerful now that a simple ReCo, because of the focus. In the long run... I don't know. On the one hand, that makes 4 arts to raise, but on the other, there's a focus.
And add Perdo Ignem free requisites. These guidelines sound more like what freezing a body would be like, compared to Rego, which is about controlling them. Plus, the Rego Corpus option goes for a whole-body assault at a fairly low level, whereas I would think that with freezing you'd have to work up somewhat to covering the entire body.
Of course, with Ars, there is a thousand ways you could do such things. You could also Creo Terram(Ignem) to encase them in ice.
The big problem here is that you want to do it in a way that doesn't kill people, and that doesn't feel very icy to me, so it requires a more complex level of control over the freezing process.
Yes and no
Realistically speaking, you're perfectly right.
But I had in mind some comics and cartoons "freeze rays", that's why I didn't add a +1 magnitude and some fatigue damage (or, more exactly, take the higher guideline and add +1 mag). I could, mind you.
I dunno the rego level, I worked from memory (IIRC, there's a guideline to hold a body motionless). Is that low?
The MuTe option might have been fine, but it is really too high level and I don't turn them to ice, I just freeze them.
PeCo 5 is fine, given a strength check to break free.