One of my players in my homebrew setting wants to create a new race of soldiers.
He wants to use creo corpus to create a soulless but living body into which he can use mentem to put a soulless and very simple mind to allow it to follow simple orders.
My query, ethics aside, can you use corpus to create a living but soulless human body and how hard is it?
Also, can you animate that body and have it follow commands as you would with a corpse (i.e. with ReCo(Me) magic)?
Well, if you can use Shadow of Life Restored to revive a soulless corpse, and you can use low level CrCo to create a corpse, it seems like combining them would do approximately what's desired.
However, you might want to do it without the mentem requisite, if you'd rather not have it have it's own mind (and risk being possessed by demons)
Creating a soulless human body is easy, Creo Corpus Base 5. You can create them with a Month duration and Group target (plus size) for lots of bodies. But creating permanent ones requires a Ritual, and hence raw vis.
Animating the foot-soldiers is also simple, with Awaken the Slumbering Corpse. The problem is creating a cheap way to animate your undead hordes. Assuming you don't need them in perpetuity, consider using Circle target and Moon duration. Cast the spell yourself or through magic items, monthly. Also consider doing the same with Charm Against Putrefaction.
Your players' goals are more ambitious. Creating a mind is not covered in the guidelines. I think it tresspasses on God, and I wouldn't fully allow it as an SG. I would allow a partial version a la The Shadow of Life Renewed, with something like the same guideline level too (70). Not a good option. At any case, it's deep into the domain of house-rules and group/SG decision.
Trapping a mind, now, that should be doable. To construct your generals, prepare the corpse for enchantment. Then invest a ReMe power to trap a ghost in it and force it to obey your commands. Then invest a InMe power to read the ghost's surface thoughts, and a ReCo power with a linked trigger to it to move the body as the ghost wishes. And your'e done - one mind, bound to the body, ready to act on your instructions with all the flexibility of a full intellect.
For your amusement, I present to you also a similar scheme from my own past, long-long ago. Warning - it's extremely unethical. It's also somewhat against the rules. The spell below can be thought of as being a part of a "Mystery" that involves creating Magical creatures through magic. It's one of the fruits of that mystery - a spell that creates the Hauweta, a rather dark magical creature created from a Trial by Fire of adulterous lovers.
Ritual of the Hauweta
ReMe (Co, Ig) 60 Ritual
R: Voice, D: Until, T: Special
This horrible spell binds the spirits and bodies of two persons as they are burned at the stake, turning them into a terrible undead creature. The two persons must share an arcane connection between them somehow. The spell intended to serve as a trial-by-ordeal for infidelity, so that it is cast on two lovers and the man’s seed serves as an arcane connection between the target’s bodies if they have truly slept together. (If they have not, the spell would fail, and the couple will simply perish in the flames.)
The two target’s bodies are tied together and they are burned at the stake as part of the ritual. The spell binds the spirits as they attempt to leave the dying bodies, forcing them back inside and imposing overwhelming obedience to the caster. It also binds the two bodies together into a single mishappen body, that the two spirits occupy together, and that has immense strength, powered by the powerful magic. Finally, the spell keeps the bodies eternally burning, inflicting eternal suffering on the wretched souls. The force of the magic is such that the poor victims are forced to obey the caster even through this suffering.
This powerful spell actually creates a Magical creatures, an undead of Might 30 called an Hauweta. Hauweta always refer to themselves as “we” and eerily speak in two voices. They are in eternal agony, but in all their actions show fanatic loyalty to the caster. Their bodies are forever burning with flames, which engulfs and ignites any items they hold. They are typically encased in strange, metal-plate armor from head to toe, which protects the environment from this damage, although it is too hot to touch and flames can be seen flickering inside it. Their hands are kept partly open, so that their touch still engulfs anything they touch in flames. They can furthermore inflict the pain that they feel on others.
(B 10, +2 voice, +4 until, +2 group, +1 Co,. +1 Ig,)
Hauweta Character Guide
Magic Might 30 (Ig)
Personality Traits: Suffering +3, Loyal (to master) +6
Strength +6, Stamina +6, Dexterity 0, Quickness -3, Presence 0, Communication -3, Intelligence varies, Perception -3
Abilities: Varies, plus Single Weapon 3 [weapon use made easier as magic wields the body directly by the will]
Soak: 15 (6+9 armor)
[Hauweta do not heal wounds. They have no Fatigue levels, and never tire.]
Sword, Long: Init -1, Atk +7 [4+0 dex+3 skill], Dfn +4 [1+3 skill], Dmg +17 [6+5 fire+6 str]
Powers: Blade of the Virulent Flame at will (by touch); can affect other items and ignite other things as well, at 0 Points, Penetration 0; Pains of the Burning Flames (B 4+1 Eye, +1 Dia) The target feels burning, agonizing pain, effect as per Weight of a Thousand Hells; 5 Points, Penetration 30.
The fact that humans have souls by default makes creating a living human / bringing life to a dead human really ridiculously hard (base 75) - whether they have a mind or no.
Of course you could just go with something much lower base using the animal arts as a guideline if the body is intended to have no mind (and obviously no soul) - but then... wouldn't it be dead?
Which raises a second question: why living bodies? Dead bodies with ReCo would be fine, and with ReCo (no mentem requisite) you can animate a corpse and have it follow your commands (see 'Awaken the Slumbering Corpse' in the core rulebook).
Also animated corpses don't suffer from things like deprivation or pain, and can function quite well even if missing what would be critical organs for a living entity.
My necromancer is working on undead 'canaries' for dangerous areas: a summoned corpse that can be avatar-d into. Enter dangerous area, get dismembered/boiled/stabbed/whatever, make relevant notes about what went wrong, try again.
Ah, I didn't notice the "living" part. Oh well. Much of the same still applies. I think creating a living soulless body shouldn't be difficult. The rest, about the mind and all, is the same as for a dead one.