For ease of reference, I thought I'd put in some quotes on the forms of spirits - Rules:
[ Spoiler ]
Spirit Attributes (SR4A, pg. 186)
"Spirits are creatures constructed of pure mana. Their power is primarily measured in their Force attribute, which describes the intensity of mana power residing in the spirit. The spirit’s Force also determines how difficult it is for a magician to summon or control."
Spirit Forms (SR4A, pg. 186)
"As a rule, spirit forms are metahuman sized or smaller and tend to have an obvious ethereal or otherworldy nature (there is no mistaking them for real people). Materialized physical forms are not subject to gravity, though most spirits (except air spirits) stay earthbound or close to it (perhaps floating or hovering)."
Spirit Combat (SM, pg. 94)
"Spirits are creatures of quicksilver and shadow and are nearly immune to physical attacks. They are also creatures of willforce and imagination, however, and can be disrupted by the sufficiently committed."
"Spirits materialize in all manner of forms, including those equipped with weapons such as swords or claws. These “weapons” are (obviously) part of the spirit’s materialized form, however, and do not provide any extra bonuses."
Spotting Spirits (SM, pg. 95)
"The spiritual nature of any materialized spirit form is unmistakable. Even if the spirit materializes looking like a toaster or a Lone Star officer, any sentient observer will have no difficulty understanding that they are observing something unnatural."
Spirit Appearance (SM, pg. 96)
"Just what does a spirit look like anyway? If it’s in astral form and you’re a physical observer, the answer is easy: it’s invisible unless manifesting, in which case its presence may be marked only by a barely discernible discoloration in the air. If the spirit is possessed into a body, the answer is equally simple: the spirit looks just like the vessel, modified by its basic spiritual presence and whatever powers it has (most of which are invisible until used, but powers like natural weaponry and energy aura are quite dramatic).
While a materialized spirit can’t be mistaken for a material creature or object, it can look like almost anything, [...]"
Realistic Form (SM, pg. 102)
"A spirit with Realistic Form can be mistaken for a normal physical creature or object when it materializes, or it appears unremarkable when joined to a vessel. A spirit that appears as a metahuman would have a heartbeat and a regular breathing rate. A spirit that appeared as an object mimics the object’s normal functionality; for example, a toaster could be plugged into the wall to toast bread (though it would have no Matrix link, making it an antique toaster)."
Free Spirit Nature (RC, pg. 91)
"A free spirit, in its materialized form, is made of energy in the form of a set of coherent forces. These forces effect the space around it, giving it the illusion of shape, mass, and appearance.
The interaction of these forces with the physical world cause light to reflect at various wavelengths, making it possible for cameras, ultrasound, radar, and other physical detection methods to perceive the spirit. A free spirit has the “look and feel” of a physical being, based on the form it took before it became free, but it is not made of the materials that appear to make it up; “skin” will not tan or sunburn, “iron” will not be attracted to magnets. The spirit has no mass, but the forces in its form have all of the effects of a body with mass, according to its Physical attributes. A result of being comprised of energy is that the spirit needs no clothes, food, or shelter to survive, although, in many cases, the spirit can wear clothing, eat food (which it can later expel discreetly), and live in a home, as the social situation warrants."
"Spirits do not need food or shelter."
Free Spirit Health (RC, pg. 93)
"Spirits are creatures of mana and have no real bodies to speak of. They can still become hurt and suffer the same dice pool modifiers for Stun or Physical damage that their metahuman counterparts do. Spirits also heal at the same rate as metahumans (p. 242, SR4)."
"First aid and medicine and medicine do not work on spirits, although they may work on a possessed vessel. Any healing or repair given to a vessel applies only to that vessel’s Condition Monitor, and not to the spirit’s. Free spirits may not use cyberware, bioware, nanoware, transgenics, drugs, or anything else that requires an organic body."
...and Fluff:
[ Spoiler ]
On the Forms of Spirits (SM, pg. 90-92)
"Spirits appear on initial inspection to incorporate a great diversity of materials into their corporeal forms, from water to bone, fire to plasteel. After decades of study, it appears that the materialized forms of spirits are not actually composed of previously recognized substances. Indeed, the studies of Halthmer et al. demonstrate basic property equivalencies in the constituent structures present in earth elementals and the spirit of Mt. Rainier. The most commonly accepted interpretation of their data is that spirits are largely composed of some kind of common arcane material regardless of apparent structure—a recombinant protoplasm that replicates function, mass, texture and properties near enough as to provide no physical difference."
"Another intriguing aspect of a spirit’s corporeal form is its senses. Despite having no nervous systems, spirits react negatively to damage to their physical and astral forms—similar to how a physical creature displays pain. Spirits frequently object to being sent into positions where disruption is likely, and when directly questioned about the phenomenon, spirits have tended to describe disruption as an agonizing event more oft en than as simple dissipation. Likewise a spirit’s sensory perception is very diff erent from our own. Even when a spirit materializes into our world, it still exists primarily as an astral creature. When observing an object, a spirit sees the auras and shadows first and the physical characteristics second.
Physical details metahumans characterize as obvious are frequently overlooked entirely by spirits. Interaction with technological display devices and simsense such as commlinks and simrigs is even more tenuous. The location of a spirit’s visual ability is at the very least variable; and as there is no nervous system to connect to, the technical difficulties of making such an AR setup are far from trivial."
This is the way I interpret the above:
[ Spoiler ]
Now, not being affected by medicines or drugs, not being able to digest food, not having a nervous system - these are all good indicators that poisons and such shouldn't work on a spirit. I know, they don't have the required immunities - unless we say that poisons etc are considered 'natural weapons' and reduce their power by Force x 2.
It's pretty clear that they don't have organs, nervous systems, sensory organs, or the like (unless they have the Realistic Form power), and thus it is less likely that 'aiming for a vital spot' would work. All of it's form is the same type of matter, and not subject to several laws of physics.
Not having proper bodies, spirits would also likely not be subject to the optional rules for severe wounds - things like bleeding, organ damage etc shouldn't really affet them.
As for sensory organs...no, not really. They don't need specific spots of their forms to be their eyes and ears - unless they have a realistic form, even eyes that they seem to possess won't function as eyes, and thus they wouldn't be negatively affected by the 'loss' of those.
They aren't physical beings; they have massless materialized forms mimicing the look and feel of different materials.
Some questions to think about:
- Do you apply Fatigue damage to spirits?
- Do you allow Nausea Gas to affect spirits?
- Do you allow the Throw maneuver to work on a spirit?
- Do you apply the rules for hazardous enviroments to spirits:
- Dehydration?
- Impaired breathing?
- Frostbite?
- How about radiation and radition sickness?
- Drowning?
- Do you think a spirit can be suffocated?