Gang, I've always played it that if the enemy don't know you are there, their Dfn roll doesn't get the ability score added, because they aren't using their skill. I was looking in the core book and can't see surprise rules anywhere.
Basically this is for the Venice thing. I'm trying to explain why a guy close by with a stilleto is so dangerous. In D&D, for example, he's not: he's just going to stab you with a bit of sharp wire, effectively, and you can shrug off a crossbow bolt.
In Ars, I thought it was basically that he got a free hit which lets him compare Dex + Brawl + 1 (Atk mod) + stress against just a stress die, so most of his Atk rolls over onto the Damage roll (which is Str + 2 (damage modifier) + Attack Advantage), which is then mitigated by Soak (Sta + Protection, but as a special rule stilletos reduce Protection from Armor by 2, because they are basically a misericorde (a knife made specifically to stab people in armor)..
After that first hit the stilleto's less useful than a steak-knife, but it only needs one. Also, you get a negative modifier to heal the wounds using mundane skills because they are like arrow wounds but worse (deep cone of trauma with a narrow mouth) and I'm going to scale that to the Brawl skill (twisting the knife so the internal injury is a broad cone, not a tube is an advanced stiletto skill)
So, to me that all seems fine and dandy, but the underlying rules aren't where I thought they were. Anyone able to point me in the right dircetion?
I don't think they're clearly stated. Page 6 and 7 that explain the basics do not include contested or opposed rolls (at least to my late at night reading). I would infer from Folk Ken vs Guile on Page 65 (Curiously, the only place "opposed rolls" are directly stated in the entire core book) for Awareness vs Stealth. If a PC or NPC's awareness fails, I would also rule that a Defensive roll isn't allowed and defaults to zero.
Clearly, this is just one of those things that's so obvious to experienced RPG player that it isn't in the corebook, and yet another minor barrier entry for those GM's who find ars magica and have never played any other game before.
That is more detailed than basic ArM5 combat rules are.
Sometimes it helps to look up LoM p.117 ff Optional Combat Rules to see, whether an option is compatible with the rule you assume. If it isn't, the author of Optional Combat Rules didn't consider your rule.
LoM p.118 Reactions defines Defense rolls as Reactions, and a "character can perform a reaction any time the storyguide asks him to". So in a surprise situation with Optional Combat Rules a storyguide can also just not ask for a character's Defense roll at all and go to damage if the surprise Attack roll was successful. That is not quite a "free hit". But it also gives you a rule for surprise attacks: uncontested Attack rolls.
We also used to have an off-hand rule, as I recall. I'm not entirely clear why historical dudes went for the single stilleto when they could have used two, because they aren't a fencing weapon: you just drive it into a guy who doesn't know you are going to attack him. I suppose its because they strike double handed, like with a rondel dagger, and get their weight in behind it.
In the movies it is because they are using their dominant arm for a sort of grapple that covers the mouth, and striking off hand with the knife, but that's more of a movie thing because as the great Christopher Lee pointed out, if you stab someone in the back and collapse a lung they literally can't scream.
For something that's taking up les than 500 words, this is proving to be a bit tricky. I originally left them out entirely because they are a 16th century thing, but I wanted cloak and dagger fighting.
I personally would noy go into such details for the stilettos, they are just another type of dagger. Lots of pother weapons were designed to bypass armour (battle picks and various hammers), so maybe just adding a "penetrating keyword" ti some weapons could work, but then why not a cutting and a bludgeoning one. Starting with one type of dagger being special starts the slippery slope towards the glaive vs guisarme vs bec de Corbin vs voulge.
That being said, it is obvious that each troupe can and should do as they wish and if there os playtested support for more combat rules, the people might as well get the option.
Oh, I'm cheating the history on so much else that it doesn't matter. 8) So, you're right, but I'm going the other way because Canon Is Not A Thing in the brave new world before us.
In LoM among the optional rules there are also some not listed as optional, meaning they're supposed to be standard and were included later. One of those rules is that a truly defenseless person has a -10 for their Defense Total. No roll, no Ability, no Characteristic; just -10. A person skilled with a dagger like this is likely to kill such a person in a single blow.
All rules outside of Core are optional. If they were supposed to be standard, they should be in the core rule book. Maybe the upcoming Ars Majica definitive will include it?
Surprise, is one of the most contentious issues you will ever see. Maybe only surpassed by how to handle wound penalties.
Some people will say -10, that's a bit harsh, use 0.
Then someone will counter saying a person with no skill and a light wound, is worse than someone not even aware of the attack. That seems wrong.
A different counter argument is, a battle hardened veteran is completely surprise, even if they miss the perception roll by 1? A battle hardened veteran should react. A better rule is to reduce the defence bonus by the difference between the perception and stealth.
A different angle is -10 isn't enough. If the target is truly surprised, unless the armour is head to toe, such as full plate, the assassin gets to hit an unarmoured location. Defence is -10 and the only soak is Body.
The other vaguely relevant bit of Rules I can think of is the "Ambush Predator" quality (HoH:MC pg 42). This says:
...If it has successfully crept up on its prey, it automatically wins Initiative in the first round of combat and gains a +3 to its Attack Total for the first round only
If you combine with exerting on your attack you can do a reasonable amount of damage assuming you're vaguely competent with the relevant martial ability, but it's far from a guaranteed kill.
There's also a similar rule in the HoH:S Flambeau chapter (pg 32) on fighting invisibly:
An invisible character can make surprise attacks against opponents who have not precisely located her (see below). During the first round only, the invisible character automatically goes first and gains a +3 Attack bonus (this combines with the usual bonuses from the Effects of Invisibility table)
Possibly also relevant is that the maximum bonus from invisibility (i.e. when the opponent knows you're there but not where) is +9 on melee attacks.
I get what you're saying, but I also dislike what you're saying. The reason why is you're saying if something was left out of the core book, it can never ever be included later. We know for certain later books have tried to add clarity that had been left out of the core book. That's why we have things like the explanation in TMRE about how much vis you can spend at different times on Longevity Rituals. Your take is dismissive of what we know David has tried to do; and as we know that was his intent in a number of circumstances, we know your take is not really what we're supposed to assume in these circumstances.
Consider: Why is it that so many LoM rules are listed as "optional" and this one is specifically not listed that way? If we're supposed to consider them all optional, what is the point in writing "optional" all over the place? And if they're all optional, what is the point of distinguishing some as optional and others as not?
I like these because being surprised is not necessarily the same as being completely defenseless, and that -10 is for completely defenseless. So generally that -10 may be too much.
Offhand I would say there are no surprise rules because there are so many different kinds of surprise. An arrow from the darkness shot into someone's back is a different situation then an attack you are aware of in the moment but didn't have enough warning to draw your weapon for defense. Different situations would need to be adjudicated differently.
I read "defenseless" as sleeping.
If you let someone fix the back of your clothing, it comes down to the same situation. But you will flinch away from any sudden movement you see coming, which may be a 0 because you get no useful reaction.
I realise that I didn't really answer the opening question.
I cannot say where in the books I might have come across it but my groups have been doing it the same way as you describe (attack+ die vs die alone), although now to go faster, we just do Attack+Damage+stress die vs soak + stress die.
Yes, sleeping, tied up, etc. That's why I said "truly defenseless." That's also why I commented above that commonly the penalty should be less than this, that the 3 to 9-point penalties may be more reasonable.
Someone else got to it before me, but yes, the only thing close to a "surprise" rule I know is the one for invisibility. I would start there if I were you.
To quote something I found in World of warcraft discussing letter openers:
As is always the case with letter openers, this is a completely useless tool, kept only as an excuse to have a murder weapon nearby in situations where it would be socially unwise to carry a dagger.
I've always thought truly defenceless, unless there is some reason the person can't easily finish the helpless individual, there is no roll, the defenceless person is dead if it is desired.