What happens if you scry a target with either scrying or greater scrying while the subject is under the effects of a (Greater) invisibility spell?
This is assuming the target fails her will save and the scry will actually go through as it would normally do to a visible person.
The spell would work, but could confuse the watcher.
If the save fails, you can see and hear the subject and the subject’s immediate 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.
The sensor itself would be created. Think of scry as revealing the location of the target, but doing nothing to the target itself. If you also had see invisibility available to yourself, you would also see the "invisible" creature.
You would see the location and hear what is going on, but likely one may think the spell had failed. If the invisible creature moved, the scrying device would move with them. Scrying itself does not specifically require line of sight in order for it to work.
The spell would work & the caster should immediately know something is up & easily figure out what it is!
If the spell fails (target succeeds it's saving throw) nothing happens. The caster knows they failed and they can't try again (on this target) for 24hrs. They can, however, cast another spell targeting any known friends/party members known to travel with them if they have such information.
If the caster is able to see an area but simply can't see the target of their scry they should know the spell succeeded and that they just can't see them for some reason. (this is similar to a dark room, the caster knows their target is there they just can't see them)
Remember
Scrying is a 4th level spell (minimum CL=7) while
Greater Scrying is a 7th level spell (minimum CL=13) and
Invisibility is a 2nd level spell (minimum CL=3).
Unless the caster had a recent run-in with an illithid he should have an idea that other magics are in play. To be 100% true to the rules you could have the caster roll a spellcraft check to identify that it's an invisibility spell (DC=22 for Invisibility or DC=24 for Greater Invisibility) but I'm also pretty sure a caster of this level has "seen" Invisibility cast before.
Additionally, there is a 5% per CL (minimum 35% chance @level 7) that detect Magic/law/chaos/evil/good & message) function through the scry. If successful, these spells will enable the caster to further identify what magics are at play and where the target is at, if not what they're actively doing.
*Note: corrected caster level to reflect wizard vs sorcerer
From the Scrying spell:
As with all divination (scrying) spells, the sensor has your full visual acuity, including any magical effects.
So, I don't think the Scrying spell changes anything about your vision (so for example, you keep your Darkvision while scrying into a dark room). As others have mentioned, you would definitely still get a sensor at their location. However, there's also nothing stopping you as a Bard/Wizard/Sorcerer from having a See Invsibility spell ready to go. Detect Magic/Alignment/etc is also an option for most casters, but unless it's Greater Scrying you still have the chance to fail.
