I have a couple of questions about the interatcions between 2 characters in a magical duel.

Character 1 is on the physical assensing his opponent in astral space. He can only attack with mana based spells.

Character 2 is a free spirit in astral space observing the physical.

first question does Astral Armor protect against Stunball?

second question can the spirit cast physical spells from Astral to target the physical side. Spells like Levitate and Lightning bolt. If so would he recieve the -2 penalty for interacting with the real world?

Thank you in advance for any answers given

1. The Astral Armor spell protects only against attacks made using the Astral Combat skill. It doesn't protect against Stunball. Your defense pool would be Willpower + Counterspelling + Counterspelling/Shielding Focus.

2. I'm not sure what you mean that the spirit is in astral space "observing the physical." If the spirit has not materialized -- which is more than just manifesting -- than the spirit cannot cast physical spells on people who are not astrally projecting/perceiving or who are dual natured. I'm assuming, however, that your spirit is contemplating casting a physical spell at Character 1, who is astrally perceiving. In that case, I think that the spirit CAN cast any spell -- mana or physical -- on the astrally-perceiving character. (I'm sure someone will correct me if I'm wrong!) As for the second part of this question, the free spirit would NOT receive a -2 penalty for interacting with the physical plane. IIRC, only a character who is NOT normally dual-natured but who is astrally PERCEIVING (not projecting) can suffer from that penalty.

You can't cast any Physical spell while in a purely astral state.
As soon as the spirit materializes it can cast any spell it wants (as it now exists on the material plane). But in Astral space only Mana spell can be cast.

You can only cast spells against targets that have a component that matches up with your state. Once you have that, you have the additional restriction of against Astral only targets, you *must* use Mana based spells (Stunbolt vice Powerbolt)

Caster State:-----Target State
Physical plane = physical plane or dual natured targets (spell can be mana or physical)
Astral plane = astral plane targets or dual natured targets (spell must be mana)
Dual natured* = astral plane, physical plane or dual natured targets (spell can be mana or physical)

*by virtue of being dual natured like a dragon or through using things like Materialization or Astral Perception. List of dual nature effects is not all inclusive

Against an Astral target the spell must be Mana as Physical spells have no effect on the Astral plane.

I don't have my books handy so I can't look this up right now, perhaps someone can help me: If a dual-natured critter gets into a fight with a spirit (that is not manifesting/possessing), do they use astral combat as a skill, or their normal attack skills?

For example, a spirit is going past a ghoul, does the ghoul use unarmed combat to claw it, or does it need to use astral combat?

I don't have a 4A book handy, but in 4e:

Of course, they didn't give ANY of the dual-natured critters the Astral Combat skill, so they're pretty much screwed by RAW.

Not sure offhand if they changed that in 4A.

The Ghoul uses his physical skills -its a tough break though because Dual natured critters are always vulnerable to astral attack and are likely to react much slower than the attacker who gets the astral initiative bonus - harsh but I guess it keeps the Ghoul population under control...

By RAW almost no critter has any skills to speak of. Check out dogs (no unarmed combat!)

??
They have unarmed combat 3 in my old 4e book.

AFB at the moment, so I can't really speak well on the subject.

Any perception skills?

yeah, perception 2, power: enhanced senses (smell)