[Beta]

I'm talking about the friendly form of possession here (not inhabitation).

Clear from Street Grimoire:

- Technomancers can't use their abilities (it says this is because you use the spirit's mental stats.  I'm not entirely sure that the one precludes the other -- but it clearly states that they can't).  This presumably also means that the person being possessed could not use an internal commlink to communicate with their team.

- A body left behind while a mage is astral projecting is a suitable vessel.  So you can be astrally projecting while a spirit runs your body, but you are not in such direct control at that point (you give the spirit orders, you aren't sitting in the backseat giving it a steady stream of instructions)

Things that I'm less sure on:

1- Once possessed, could a mage start astrally projecting (i.e. start off in their possessed body, then leave?)
2- And vice versa of 1 -- if they are astrally projecting, could they return into the 'back-seat' of their body (say to avoid astral combat, give better directions to their spirit, etc).

3- Use their knowledge skills, make memory checks, etc.  If yes, do they use their normal mental stats or those of the spirit?

4- Sustain a spell (that was cast before possession started).  For example, could a mage apply improved invisibility to their entire team (building up a huge dice penalty), then have a waiting spirit take over their body to do things?  Would it matter between regular sustain, focused concentration, and a sustaining focus?

5- Have the spirit use a DNI? (say you have trodes on, and a team-member sends a message to your commlink that you would normally receive via the DNI.  Does the spirit or mage receive it?  Or is it just a burst of meaningless static to the spirit, and hence also to the mage?)

[Marcus]

1- Once possessed, could a mage start astrally projecting (i.e. start off in their possessed body, then leave?)

This is kinda tricky, as presumably when one isn't using your mental attributes your probably not awake from system point of view. But if this came up at my table I would still go with probably, given that it's friendly possession. I assume the possessing entity can give you a sec to get going on your little astral romp, but that's a big assumption on my part. So under strict RAW I'd say No.

2- And vice versa of 1 -- if they are astrally projecting, could they return into the 'back-seat' of their body (say to avoid astral combat, give better directions to their spirit, etc).

Yes again, what would be more interesting question is what happens when you start taking astral damage and the body is possessed? Does that body soak differently from you with another spirit involved?

3- Use their knowledge skills, make memory checks, etc.  If yes, do they use their normal mental stats or those of the spirit?

If they were projected i would say yes your normal mentals, if not then no.

4- Sustain a spell (that was cast before possession started).  For example, could a mage apply improved invisibility to their entire team (building up a huge dice penalty), then have a waiting spirit take over their body to do things?  Would it matter between regular sustain, focused concentration, and a sustaining focus?

I would go with no. Once your out from being possessed your no long valid portion of the casting equation.

5- Have the spirit use a DNI? (say you have trodes on, and a team-member sends a message to your commlink that you would normally receive via the DNI.  Does the spirit or mage receive it?  Or is it just a burst of meaningless static to the spirit, and hence also to the mage?)

The spirit get the msg as it's in-charge on the cells that received it.

[SpellBinder]

My take:

1:  I'd say no; once possessed you're now a back seat driver (if you were conscious) and all you can do is watch.
2:  Also, no; if you want back in your body you gotta get that spirit out first.  Astral combat might not be the best option if the astral damage will spill over into your meat body, but then there's also Banishing that seems to be frequently overlooked.
3:  I'd say the person uses their own brainpower for this (their Mental attributes & skill).  But without any way to record notes the person's stuck using their own brainpower to remember everything.
4:  If you can't cast a spell while being possessed, then I'd also say you can't sustain it either.
5:  No.  Spirits are considered alien when it comes to that kind of tech, and they don't really have any anatomy, so can't use anything that isn't more simply voluntary (like basic cyberlimb movements) or automatic (like bone density augmentation or bone lacing).

Now with all that covered, look into the metamagic Channeling.  It allows any summoner to be possessed by their own spirits and still retain control of their body (even those of traditions that don't normally have possessing spirits; their spirits can only possess their summoner).  In this context then some things like using knowledge skills and DNI (and with it AR) change because the summoner has joint control of the body and their mental faculties can still interface with the tech; they'd also be able to still sustain their spells.

[Beta]

Spell binder, on point if you are the summoner you can do somewhat more than watch ... but it is still admittedly a bit like being a plays director in that you may give directions but you don't act.

On point two, if it is your spirit of course you can easily get the spirit out, you just tell it to do so!

[SpellBinder]

True both, but part of my thinking at the time of the post was that the possessee was not the one that had summoned the possessor.  It makes things much easier when the summoner is of a possession tradition and using his/her own conjured spirits for self possession for that little extra oomph to take things to 11.

[Reaver]

I'm talking about the friendly form of possession here (not inhabitation).

Clear from Street Grimoire:

- Technomancers can't use their abilities (it says this is because you use the spirit's mental stats.  I'm not entirely sure that the one precludes the other -- but it clearly states that they can't).  This presumably also means that the person being possessed could not use an internal commlink to communicate with their team.

- A body left behind while a mage is astral projecting is a suitable vessel.  So you can be astrally projecting while a spirit runs your body, but you are not in such direct control at that point (you give the spirit orders, you aren't sitting in the backseat giving it a steady stream of instructions)

Things that I'm less sure on:

1- Once possessed, could a mage start astrally projecting (i.e. start off in their possessed body, then leave?)
2- And vice versa of 1 -- if they are astrally projecting, could they return into the 'back-seat' of their body (say to avoid astral combat, give better directions to their spirit, etc).

3- Use their knowledge skills, make memory checks, etc.  If yes, do they use their normal mental stats or those of the spirit?

4- Sustain a spell (that was cast before possession started).  For example, could a mage apply improved invisibility to their entire team (building up a huge dice penalty), then have a waiting spirit take over their body to do things?  Would it matter between regular sustain, focused concentration, and a sustaining focus?

5- Have the spirit use a DNI? (say you have trodes on, and a team-member sends a message to your commlink that you would normally receive via the DNI.  Does the spirit or mage receive it?  Or is it just a burst of meaningless static to the spirit, and hence also to the mage?)

1: From my understanding, if you allow, or are taken over by a spirit, you become locked into your own body, you can't act, move, cast a spell, or any other action. Basically you are along for the ride as your body does whatever it chooses with (or TO!) your meat suit.

2: AS someone else noted it is possible for your body to become possessed while astral (Shedim!). And now you are screwed! With out a body to return to, your astral form will dissipate, and you die. And chances are that if someone is wearing your meat suit, it's not where you left it - and now you can't find it! Once you find it, you going to have to fight to get it back. (Generally. Spirits that body snatch are not known for willingly returning said bodies).

3: you could use your knowledge skills and memory checks (with the character attributes), but that isn't shared with the spirit. Just because the character knows he is fighting Corp Security from Ares, doesn't mean the spirit does - or cares. now the the character could pass on that knowledge to the spirit as a "suggestion", but the spirit doesn't have to act on it. Only the summoner has any amount of control over the spirit.

4: Spell sustaining takes an amount of physical and mental effort, something your body is no longer capable of. Remember that you are in the backseat of your body, the meat under the full control of the Spirit... right down to what your eyeballs focus on. Think of those crappy shaky mobile phone videos posted to youtube all the time, all you see is what the camera is pointed at (in this case, your eyes).

5: Spirits and tech do not match. Ever. Some cyberware gets past that statement just because it's so tied to your natural form however. (like a cyber arm.) But generally speaking, if you didn't pay essence for it, a spirit can't interact with it.