I feel like this might be a specific question, but I'm not 100% sure about it, so I'll describe the exact circumstance and wonder about the overlying rules.
This character is a Drow Vigilante, with Drow Nobility (and later Improved Drow Nobility). The Vigilante ability Startling Appearance states the following:
Whenever a vigilante with this ability attempts an attack against a foe that is completely unaware of the vigilante’s presence (usually due to Stealth or invisibility), the foe is treated as flat-footed for the rest of the vigilante’s turn (uncanny dodge or a similar ability prevents this effect unless the vigilante is at least 4 levels higher than the foe with uncanny dodge).
The foe also takes a –4 penalty on attacks made against the vigilante until the start of the vigilante’s next turn.
I'm having trouble wrapping my head around what "completely unaware" entails, since it specifies Stealth.
Drow have Darkness as a racial spell, which reduces the light level, and later Deeper Darkness will reduce it by two. If the Drow drops a darkness bomb, reducing the light level to darkness (or lower), line of sight is broken and total concealment is gained (assuming the victim doesn't have Darkvision or another sense). However it seems logical that someone could feasibly realize "she's in there somewhere", thus making them not completely unaware of the vigilante's presence.
So this is my dilemma. Where does the concept of concealed end and unaware begin? Can this ability only be used as an opening gambit, or does it work like a Batman: Arkham game where you can dip in and out of the shadows terrifying people? (Frightening Appearance at 11th level adds a 10 ft radius Intimidate to the Startling which is what I mean by my comparison there)
Ever played any stealth video game Skyrim?
The moment you drop an enemy from stealth, the remaining enemies draw their weapons and investigate the surrounding area. You're still in stealth until they find you, and if you're quick you're able to kill them all before they can reach your hiding spot.
The first enemy was 'completely unaware' of you. The rest not so much.
Why it specifies Stealth is that your opponent needs to be completely unaware of you.
Let's say you've disguised yourself as an arms dealer trying to strike a deal with the local ruler. When you were supposed to showcase the accuracy of your longbows, you "accidentally" turned 90 degrees and shot the king in his throat (With a successful Disguise/Bluff check for triggering a Surprise round). While the king and his guards were really surprised (and Flat-footed), they were all still aware of your presence. Ergo, no Startling Appearance.
Edit: I think the 'states of awareness' are described in Ultimate Intrigue, p 188.
Isn't there also a clause somewhere connected to completely unaware that the creature can also think of you as an ally?