Can a being not on the (Prime) Material Plane Astrally project? I mean, create an Astral body with a silver cord and then form another body on another Plane, the way someone doing it from the Prime can? Could (say) a Giithzerai cast the spell, go Astral and then form a new body on the Material, with his original safe at home on Limbo? Obviously, he could physically visit the Astral or Prime, but that not what I mean...
Reverse Astral Projection...
Baseline illithids used to have the astral projection ability. I'm thinking they lost it in 3.5 specifically because of abuse of "reverse" astral projection.
Based on some Internet posts I've seen, a lot of DMs would have their illithid baddies astrally project into the Prime Material Plane (so you would never be able to kill the illithid's physical body, which was somewhere else). I don't think that was ever intended -- I think it was just one of their powers so that an illithid could visit Outer Planes either physically or astrally, as opposed to projecting into a Prime world. (Both have their risks, since githyanki, some of whom have silver swords, infest the Astral.)
Not sure whether the projecting illithid's physical body was on an alternate Prime, the Astral Plane, or an outer plane.
BoGr Guide to Missile Combat:
1) Equip a bow or crossbow.
2) Roll a natural 1 on d20.
3) ?????
4) Profit!
You can go astral on any outer or material plane. Inner planes have no link to the astral, and outer planes have no link to the etheral.