Curious about what a Crystal Ball actually sees. If a target is with a party and fails it save, can you see who they are interacting with (even if those creature/people are not the target)? Can you spy on the Mage by targeting his apprentice?
I have a situation where a party wants to try their crystal ball on a person they have only seen in a disguise. If that person is not wearing the guise, does it work (if the person fails the save) - showing the person as they really are? If a target successfully imitates another person through disguise and magic, would the crystal bar target the imitator or the imitated?
If that person was being carried by a Golem (with perfect spell resistance against scrying) - would the crystal ball user see the Golem - what do you see in a crystal ball when the target is in a group?
Need some clarity....
A crystal ball just does scrying:
You can observe a creature at any distance. If the subject succeeds on a Will save, the spell fails. The difficulty of the save depends on how well your knowledge of the subject and what sort of physical connection (if any) you have to that creature. Furthermore, if the subject is on another plane, it gets a +5 bonus on its Will save.
[...]
If the save fails, you can see and hear the subject and its surroundings (approximately 10 feet in all directions of the subject). If the subject moves, the sensor follows at a speed of up to 150 feet.
So you can scry the apprentice and see the mage if the two are within ~10' of each other, and same for the party.
I'd have to say you can see the golem if you scry someone near it, though some GMs might rule the other way.
Disguise is a gray area. Expect massive table variation. I'm not even going to venture a guess as to the common case.
Its a fun one -- part of me thinks a good disguise as someone else should show the someone else in the crystal ball (unless the someone else makes the save), as the user of the crystal ball's awareness seems to be the measure of save DC. If you aware wrong, the result should be wrong. As for plain old disguise, not trying to imitate a particular person, I am going to go with the idea that the crystal ball's user has a weaker true awareness of the subject and give the subject +5 on the save.
As for that 10 foot area around the subject -- would this be a way to thwart Non-Detection? That spell makes it more difficult for a scrying to work if the subject is the target, but (unlike Mind Blank) it says nothing about being in the area of another target who is being scryed.
I agree with your logic on the contrasting text of mind blank and nondetection; scrying someone next to someone nondetection'd should show them both.
EDIT: Then again, nondetection specifically applies versus clairaudience/clairvoyance, which is basically always showing you people who are just in the neighborhood. So maybe the crystal ball should have to make a caster level check to see them standing next to the targeted guy (while with mind blank they don't even get to check).