I have the Ars 5th core book only. Been playing Pathfinder with my group and we are looking for something different. I have a few questions about spell design.
p.135 Trap of the Entwining Vines: You can make a quickness-Encumbrance roll to avoid or a Str roll to break out. Where are the guidelines for these 'saving throws'? Many spells do not have a 'save' to avoid and some do? how does one decide if it should or shouldn't allow a 'save'?
p. 138 Strike of the Angered Branch: It's attack score is Perception + Finesse. Why? It's Damage is +10. Why? Where are these guidelines at?
Welcome! Youll never stop having wuestions on spell design.
I don't think there are any guidelines for the rolls to avoid or break out. I'll say a bit more later.
If I recall, it is a legacy spell from previous editions. Rego attacks are based on Perception +Finesse if they can be dodged or otherwise defended. There aren't any damage guidelines for non Ignem attacks. [strike]MIT[/strike] It has been discussed here many times that Ignem is the most efficient form for delivering damage and that unless a spell or guideline specifies other, forms do the same damage for about 5 levels more in the guidelines. I might be getting that wrong. I'm claiming noble's Parma (going from memory and not taking the time to look it up).
There are some Rego spells that automatically hit such as Wielding the Invisible Sling, and unless the target has Magic Resistance the recipient rolls +10 damage and compares it to a soak roll.
Determining whether a spell should have some sort of avoidance is an Art, area spells like the first spell should give some chance for getting out of the way.there isn't anything hard and fast about it. One thing you'll find is that Ars combat is bloody and brutal and characters trapped will be quickly killed.
There aren't really any specific guidelines for the situations you've described. This is because most spells are designed in such a way that they inflict their harm directly upon the victim in such a way that Soak is the only means of resisting harm.
In the first example, the roll spell isn't holding the victim, hgowever, it creates vines which do so so the SG must decide how difficult it is to break the vines. In the second instance, the magician is using magic to swing a branch at an opponent - there's no real damage guidelines outside of Ignem, but in this instance I'd direct you to the damage for Cudgel (pg 176) and suggest the the magic has a Str of +3 or so = +10 damage.
Also, remember that Soak is rolled vs. magic. I used to forget that when I was getting started...
The answers above are all good. I'll add one bit of general advice: the Ars Magica ruleset is less exact than the D&D/Pathfinder ruleset. Be ready to make more judgement calls, especially on spell design.
You just do that, as much as you need. There are people on this forum who have played countless of hours for years on end, and know the rules forward and backward. You can even be so lucky as to get an answer from an author who wrote the thing.
Damage from weapons is not rolled. You use the attack advantage + damage bonus and compare it directly to the Soak total to calculate the level of wound that you cause.
When you attack with magic with a non-aimed spell (so, no Attack total is generated and Defence is not used) you roll for damage AND for Soak. So a Pilum of Fire doing +15 damage causes D10+15 damage. this is compared to a roll of Soak+D10 to see what level of real damage you are causing.
ArM5, page 181, 'Injuries' talks about 'Non-Combat Damage' and 'Non-Combat Soak'
When you fire arrows or hack with axes you use normal combat rules. Roll Attack, compare with rolled Defence, Attack Advantage is added to Damage modifier (for Str + for weapon) and compared to Soak (Stm + Protection + others). Notice that there is only one die roll on each side of the exchange! Atk+ and Dam on one side Dfn + Soak on the other.
When you fall off a building, step into a bonfire, or have a Pilum of Fire hurled at you there is no Attack/to-hit. So you roll 'Non-Combat Damage' which is Stress die +X. This is compared to 'Non-Combat Soak' which is Stress die + Soak modifier. So here you also have one - just one - die roll on each side of the exchange.