One of my players want to play a maga with some capacity in create/invocate and control some magic creations (like a golem, elemental, or something like that). The creations must be temporary (sun duration or concentration).
I don't find good guidelines for handle this, and don't find some similar spells ont the 5th edition of the book.
Have you an idea for handle this with the Ars Magica spell system ?
Sounds like this is best done with a spell that controlls elements. What you create will not have a mind of it's own, but will be entirely under the controll of the magus. Think of this in a similar way to the spells for animating dead.
The easiest method would be to use the Animae Mystery of House Merinita, which permits the caster to create temporary faeries out of glamour. However, this is difficult for a player to achieve, since it is one of the inner mysteries of the house. However, there are ways to permit this.
The other way is to use Muto spells to craft matter into a human-like form, and then animate it with Rego. You could combine this into a single spell, with replicates.
For example, to craft mud into a human form would use the MuTe base 4 guideline - change dirt so that it is highly unnatural. Since the guideline for animating the mud-golem would be ReTe base 3 - control or move dirt in a very unusual fashion, this will be a MuTe spell with a Re requisite (always take the higher level spell). Add 2 magnitudes for Voice, 1 for Concentration, and 1 for Part (unless the mud is in a box and not part of the earth when the spell is cast):
Magical Man of Mud
Muto Terram 25
R: Voice, D: Conc, T: Part
A patch of mud forms into a man-like figure, which can move about at your unspoken mental command. The mud figure can be up to Size +3 (depending on how much mud is available), at its maximum size it is 12' tall. However, being made of mud it cannot carry or lift anything, nor do any damage on striking someone - but they will get very dirty!
(Base 4, +2 Voice, +1 Conc, +1 Part, +1 requisite)
If the mudman was a bit more solid, he might have a low Strength score and allow him to be a little more useful.
A stone-based version would be Size 0 (the base Individual of stone is 10 times smaller than that of dirt) and a magnitude higher (to affect stone). I would count his fists as maces, using the caster's Finesse instead of Single Weapon. His Soak would be immaterial - he's made of stone.
Of course, these spells require that there is sufficient raw material around. You could always have a separate spell to create suffient raw material first.
Why not use the RoP:Magic guidelines for Elementals? This sounds like excately what you want. IDHMBWM but the base guidelines are something like Cr[Form] Base 25 to create an elemental from [Form] matter". And Base 5 Re [Form] is needed to control such an elemental.
And yes, a great concept. I want to try that out one day.
Having RoP:Magic and reading it - namely the parts about Elementals and such - will really help you. Especially with how you differentiate between Elementals (physical manifestations of an element) and Airy Spirits (the spirits inhabiting physicao objects like lakes, mountains etc).
BTW using the guidelines for Elementals, remember you need to Penetrate. And the greater an Elemental the greater its Might.
You do not need a very powerful elemental to anmate a bunch of material, though.
If you just want to control manifestations "as if they were elementals" (but be pure elements controlled by you) you could have a combo of 2 spells:
Create the material to be enchanted, or suummon it.
Animate it so that it has some form of initiative itself (well, able to perform the acts he is ordered to perform) and ther eyou go
There is at least an official magus (Severin, from Tales of Mythic Europe) that can do that with wood sculptures he creates (he animates them, so he basically has stupid bur reliable servants for Sun duration).
Hmmm.. so another question: when i control with Rego, the material i control can become "soft" ?
For exemple if i Rego/Herbam wood sculptures, they are no articulations, so they can just magically jump ? ^^ Or the wood become soft and elastic for animate them ? Maybe with a Muto Req ?
Rego magic can make stuff move in any way it is capable of - i.e. a tree or a sword could bend, but a stone could not.
Sculptures of hard wood would be hard to bend in such ways - they can still move (after all, the force moving them is external, not internal in any event), but not really change shape. A muto requisite would allow the sculpure to become more flexible.
Wihtout having the book in front of me (but some notes about the guidelines) I guess than the 'element' is earth and does not distinguish between types of earth. But it is dirt, not metal, stone, glass or gemstone. Personally I'd consider allowing the other types at higher magnitudes, although it's beginning to sound like types of Golems from 'that other game'. But Aquam, Auram and Ignem don't have these opportunities, so I'm inclined to only allow dirt with this in mind. Otherwise I'd have to allow Aquam elementals made of other liquids than water - like wine or even worse: poison or acid! I think not.
I'm not in agreement that a diamond elemental sounds cooler, not to me it doesn't. It reeks of 'fantastic fantasy' rather than 'medieval/historical/mythical fantasy' that I see ArM being. The original idea of the four elements calls it 'earth', and that's what I'd use. I might be convinced to also accept stone (at a higher base guideline, because stone normally is harder to affect than dirt). But the more I think about it, not the others.
I don't necessarily see the 'higher' grades of Terram with higher might than dirt. For the sake of the argument, suppose I allowed a diamond elemental, its Might would be based on the power and size. So a pocket version of it might be lower might than a huge dirt elemental made from an entire hill. So since the 'grade' of terram affects the level and the might affects the penetration needed, a huge/powerful diamond elemental would be very difficult to control.
I'd rather give them different abilities, because dirt is different from iron which is different from diamond. But Earth is opposite Water, and while I see a dirt elemental being washed away and turned to mush, I suddenly see the iron and diamond one be completely impervious to this. Which is contrary to the elemental theory. Which IMHO should indicate that Aq spells are good defence and offense against a Te elemental.
But I really don't recall what Might created elementals get.
The canon answer is that an elemental must be created from pristine elemental matter which already exists. Thus a "diamond elemental" - actually just an earth elemental - will probably be Size -15 and have a Might of 1 (since Size and Might are intrinsically linked for Magic Things), although it might have a very large Soak. If you found a diamond the size of a person then it would be Size 0, but only then. You couldn't have an acid elemental, because (AFAIK) you don't naturally get pools of acid unless in particularly extreme localities. This is all from RoP:M.
Also be aware that rarefying an elemental is a ritual spell, which is beyond the OP's question. I don't think the player is looking for permanent servants. That is not to say that the elemental guidelines could not give you an idea on the game stats of such critters, as another poster suggested.
If you go to the Atlas page for ArM5 and look in the right-hand column, you'll find a .pdf that contains guidelines from the supplements. That includes the RoP:M guidelines for elementals and well as other related guidelines. I still need to go through Thebes to see if there are any new guidelines, and my version has a single update to what's posted on the Atlas page, but the one on the Atlas page is nearly complete.
This would be rather a problem with using elementals, since once created they tend to stick around until they are destroyed.
Oh, and for the though of a diamond elemental - this works just fine - as long as you have A LOT of diamonds... (there is no requirement that an elemental consist of a single item). Would be a great story though - just a tiny bit of said elemental would be worth a fortune...