Outside of conflict I usually pretty much hand wave the duration of veils, because they would be utterly useless otherwise (they would drain the mental stress track really fast and at least my players wouldn't ever use them again out of conflict). Maybe that's my mistake but like I see it this is in par with the canon. As the ambush situation is a conflict starter, the relevance of this limitation is somewhat rendered mute.
I'm with you on this, even inside of conflict sometimes (though usually only when the veil is being used avoid conflict). If you've ever tried to use a veil you'd know that it's a lot harder to use a veil to achieve something when you have to worry about exchanges and duration. When it's not going to be game breaking I don't worry about the duration.
@belial666: You first point seems interesting and makes sense to me. If a veil gets stronger it seems reasonable that it should be easier to detect with supernatural perception. Problem is that this isn't in the rules. A block versus perception is always a block versus perception. It doesn't matter if it is supernatural perception or not. Rule wise if the block is strong enough, it won't be broken and we are back at the starting point. Secondly what @Taran stated is right. I'm aware of the possibilities by witch a veil may be circumvented. But that isn't the point of this thread...
I think belial is merely trying to point out that it is weaker in some circumstances, and I would agree. If your veil is 6-8 shifts that's going to block most people's alertness rolls, but if someone's already got a +4-6 (+2 for supernatural senses and probably at least +2 for gear, etc) before you even factor in their lore (which will be high) then it makes it much more likely that they'll pierce it.
I run veils the way Billy's sidebar comment recommends: not charging shifts for duration, and just allowing them to persist (usually a scene or so) until pierced.
I would rule that
a) the Veil substitutes for the Stealth roll for setting up the Ambush
b) the first attack "pierces" the veil (though I would allow a player tagging an environmental Aspect like "Darkness" or "Fog" to rule that the attack didn't pierce the Veil - and even then, the target would still be able to defend against the next attack normally)
But what if a Stealthy character is veiled? Surely they can Ambush better than a clumsy character? Yes, they can: Maneuver to set up an Aspect like "Professionally Placed" or "Devastating Backstab" using your actual Stealth skill.
Agreed on all points Devonapple. I think there might even be RAW backing for the attack breaking the veil, but I don't remember. Also, it's still an option for them to roll stealth and they can take the higher of the two.
My thoughts follow thusly; When Murphy and Harry discover Molly at the beginning of the crime scene in White Night they list off all the clues she gave away while veiled that allowed them to detect her (creaking floorboards, her perfume, ect.) but they didn't see her at all. So veils are blocks against sight, not necessarily the other senses. (more on that in a bit). During Small Favor, footprints are clearly left in the wake of a veil, another clue. Thus while a veil is helpful in setting up an ambush it's by no means foolproof.
Consider this: Molly is really only capable of generating a few shifts for an evocation spell at that point in the series. Harry and Murphy both have pretty good alertness skills. It's not tough to beat a block of 2 or 3.
This is a very important limitation on veils that needs to be remembered. Needing to roll Alertness yourself to see your target makes ambushes at least a bit harder.
I don't like the concept of having to roll alertness to see your target for two reasons. 1) the veil makes it harder to see, it does not make it impossible to see. Seems ridiculous to create something that makes you invisible, but also makes the world just as invisible to you. 2) If you have to roll to see if you can roll things get a bit frustrating. It's just not good game mechanics, too many rolls, etc.
Having said that I would definitely give a penalty (likely 2) to their shot or a bonus to their target's defense.
Really I don't see anything game breaking about allowing the ambush rules to apply to veils so long as you aren't allowing them to maintain those veils after the first attack. They get a really good first attack, maybe in the situation you outlined he takes them both out stealthily (assuming they're both mooks) and then he has to either take time and energy to create another veil, or we move on and there's conflict. Additionally I don't think I'd allow them to use the ambush rules mid conflict. An ambush really does mean that the enemy is
completely unaware of you. After that first attack they're on edge and trying to be ready for the next attack. You might get a bonus to your attack if you're veiled but they aren't going to defend at zero.