Static and Dynamic Targets

Games Discussion Ars Magica
1

I've had a go at writing up the general version of static and dynamic targets, and it seems to require a particular answer to the question about growing targets as well. What do people think?

Static and Dynamic Targets

It is possible for most spell targets to change while a spell is active. For example, an Individual person includes that person’s hat, but they can take the hat off and put a new one on. The hat they removed is no longer part of the Individual with the person, and the hat they put on now is. Spells can work in one of two ways.

First, they can affect any part of the Target at the time of casting, and continue to affect those things even if they cease to be part of the target. These are referred to as “static targets”, because the target does not change while the spell is in effect.

Second, they can affect any thing that is part of the Target during the spell's period of effect. In this case, things that cease to be part of the target cease to be affected by the spell, and something that becomes part of the target is affected, until it leaves or the spell expires. These are referred to as “dynamic targets”, because the target may change while the spell is in effect.

The way that a particular spell works is fixed when it is designed, and cannot be changed by the casting magus, although a spell working in one way is similar to a spell that is identical apart from working in the other, and so knowledge of one gives a bonus to inventing the other.

For example, a spell to make someone invisible, with Individual Target, can work either way. With the static version, if the target removes her hat and puts it down, the hat remains invisible. If she puts a different hat on, that hat remains visible, and appears to be floating in the air. With the dynamic version, if she removes her hat, it becomes visible when she puts it down, and a different hat becomes invisible when she picks it up. (The spell would cover small carried items, so she does not need to put the hat on.) These two versions are two different spells, and a maga who wants to cast both (and cannot reliably cast them spontaneously) needs to create two spells.

Static spells continue to affect the original target for their duration, even if the target changes so that it would no longer be a valid target for the spell. In the example above, the hat and person no longer constitute an Individual, but the spell remains in effect on both. Similarly, a static spell cast on a Group of grogs would continue to affect all the grogs even if they mingled with a crowd.

Dynamic spells fail if the target of the spell ceases to qualify as a target of the spell. The invisibility spell in the example continues to work because the Individual target does not cease to exist because she changes hats. However, if a supernatural effect made her grow too big to be affected by the initial spell, it would fail. Similarly, a dynamic spell cast on a Group of grogs would fail completely if they mingled with a crowd, because they would no longer form a Group.

In some cases, it may not be clear whether a target has changed or ceased to exist. Troupes should decide these on a case-by-case basis.

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2

If I understand well, a Dynamic spell cast on a valid target (at the time of casting), will be put "on hold" if the target becomes illegal (through a growth spell for example), but would resume if the target becomes legal again, as long as the duration of the spell permit it.

Example: human size targer become invisible with Sun duration, grows to size +2 (for Diam duration), becomes visible again, 2 minutes later, shrinks back and becomes invisible again.

It adds an additional parameters to some spell (Dynamic/Static), but it gives interesting flexibility in spell design.

Another point to make sure I understand your intention:
A group of grogs get Doublet of Impenetrable Silk (dynamic) cast on them. Greg the grog arrives a bit later, while his friends are still in formation and rejoin the ranks. Does he gets the benefit of the spell?

(As a side note, it will be ill-advised to design combat spell group as Dynamic, since during a fight, ranks will break and the definition of group won't apply anymore).

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Are you going to errata 90% of the spells in the game to say which is which? I mean, some are clear but aren't.

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So, I could cast a Group spell on just myself at the time. Then I might walk into a room and it would affect everyone in the room with me. Then I might walk into another room and it would affect all them instead. (All assuming the confines of these rooms make the people inside qualify as a Group.) So I can cast Group spells ahead of time without knowing who will be in the Group, as long as that's how I design my Group spell, right? Is this really what is desired?

This would require an erratum (maybe a few) in at least HoH:MC. I'm not saying that means don't do it, just that we want to keep that in mind so if it's done it gets done consistently.

Temprobe is right that this could affect a great deal of existing spells.

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I think most spells where there is a question would exist with both versions.
as I understand the directions you would not be able to cast a group spell on yourself in that way because you have to define a group, not an individual. that could become tricky in terms of what were allowed parameters- for example a member of a unit where they have all trained together but who wasn't there when the spell was cast as opposed to "the gate watch" which could cycle through people depending on who is on duty. Would the group be able to be defined by parameters like uniforms (so it could be infiltrated after it is cast)? If I cast a group spell on a bunch of people on a pub crawl and they split into three groups, none of whom is the majority does the spell fail, or does it simply stick with the largest group?

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No need for Errata. That chapter is already to long to read, and confusing (why is this rule written? Is it important? ...).
If such a problem comes up while playing, it is enough to let the group decide. "Here" nobody want to study a rulebook first - we like to play. And in > 20 years of playing it was never a topic in my groups ...

7

Yes.

Also true. I think most spells will make most sense as static, but illusions will make most sense as dynamic.

No, they could be either. Troupes can define based on how they have been playing.

You could, but then you would define the Group, and the spell would not affect anyone else. It's a Group with one member, which is legal. (Is "me" the same group as "me and several random people in a room"? No. Is this the same group of grogs if one member leaves? Yes. Is it the same group if one member swaps out? Yes. Is it the same group if it splits into three groups of two? No.)

I would say it fails, but that is explicitly left up to troupe discretion.

Note that a Group is defined by physical proximity of the members, and separation from all other things of the same type. You might well be able to cycle through a complete change of membership, one at a time, while keeping the Group in existence. You can certainly do that with dynamic Room spells, which have the same level of Target parameter, so this may not be a big problem.

We need to be sure it requires an erratum, rather than revealing that the spell is implicitly one or the other. We need an explicit description that assumes one interpretation, but does not work under the clarification. I suspect that this will not affect very many spells.

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I would find that unacceptable in one of my own sagas and house rule this out.

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The most unbalanced aspect of this I could visualize is using a dynamic spell for a continuing attack on an enemy position. For example if I define a group as being the people defending the gate of the castle and cast a PeCo spell that causes a medium wound every round then as replacement troops come to reinforce the defense it will injure them as well. That suggests to me that it should at least require another level of magnitude for such a situation.

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Nah, to me it means that you are targeting indidivuals you may not even knew existed at the time you cast your spell, may have been completely outside of your range, and that you may have had no way to target.

Which breaks the limits of Hermetic magic in... oh so many ways.

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How is that different from "individuals you may not even knew existed" until they entered a T:Room? Is it because defining a Group is an explicit/active act whereas a Room is an implicit/passive one?

That would mean that Group is in the eye of the beholder while Room is an absolute shared by everyone.

I think it makes sense that 3 magi casting at the same T:Group would get different results because they don't perceive some members of the actual group.

EDIT: I'm also thinking of an evil case where you cast a dynamic group at defenders, cast another spell to see through wall, then realize there are 20 defenders and your spell fizzles. I'm uneasy about this whole thing because actively updating the member of the Group should require T:Concentration if you need to perceive the dynamic changes.

12

As Tugdual points out, this is no different from Room.

Groups are not supposed to be explicit and active. The caster does not get to decide who is in the group: they have to actually be in a group, clearly separated from other things of that kind. You can't, canonically, cast a Group spell on "the people in that crowd wearing our covenant uniform".

You can't do that, because that isn't how Groups work, and never has been. If there was a well-defined Group defending the gate, you could cast on them, but the spell would end when they scatter to take cover from the mysterious attack. (And, if they know about Hermetic magic, they scatter to break the Target.)

However, now that I come to check, Groups were explicitly static, so this would be a change to that rule.

The core Targets that are not Containers are Individual, Part, and Group. ArM5 explicitly says that Group is static.

Individual works perfectly well as static, although there are cases (illusions, particularly) where dynamic makes more sense.

What would it mean for Part to be dynamic? The whole point of Part is that you can define an arbitrary part at the time of casting. I think this has to be static.

That would push us towards non-container targets being static, and only container targets having the option, as in the previous errata. I think we do need dynamic container targets, because it is so, so natural to think of a T: Room spell as affecting the things in the room — without adding "at the moment the spell takes effect, even if they leave the room afterwards".

If the targets are static, then the spell remains in effect, and controllable, on the target, even if it no longer qualifies as the target. That is, if not quite explicit, at least very strongly implied for Group by RAW, and it would be unnecessarily complex to have different rules for different Targets.

How about this?

There are three types of target: objects, containers, and senses. The object targets are Individual, Part, and Group. A spell cast on an object Target affects the things in that Target for the duration of the spell, even if they change so that they would no longer qualify as a valid target for the original spell. If the caster is within range, she retains control of the spell, if the spell allows such control.

Containers can be static or dynamic, and senses are their own thing.

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13

I like the idea of dynamic spells but I think it can only affect minor parts, such as your invisible hat example, and not new complete targets, such as more people joining a group. I am not sure how this gets worded. I do think containers are different and easier to rule than that but that is because they are considerably different, the container itself is relatively static and we can easily decide something has been added or removed from it. A person steps outside of the ward, an animal enters the room, an object placed in the chest, etc.

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If the group scatters the spell would fail, but if the group simply received reinforcements as it's members began dropping then it would be maintained if dynamic.

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There is a key difference between the two, in that the room itself is a clear anchor to the magic. The group, as defined in this thread, could change its composiiton several times, so much so that none of the original members might remain in the group. To what does the magic anchor itself?

Also, at the time of the casting you can sense at least part of the group, in the same way as you can sense at least part of the room. The unsensed part in both case are already there, in the same way as seing the hand of someone would allow you to target an individual.

And yes, T:Room explicitely allows affecting things coming inside to be affected by the magic when they enter the room, but rooms are a container with clear boundaries. You can definitively tell when someone enters or exits a room. That is not the case with T:Group -- its boundaries are rather amorphous, there is much interpretation needed to decide who is part of a group, and those boundaries change all the time.

I like it much better, but I would suggest that containers should always be dynamic. The magic only affects what is inside the container, while it remains in the container, because the magic is anchored to the container. It also establishes a clear and simple difference between them.

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Intuitively to me, a Group needs to be static. While I could see things/people leaving the Group, anyone joining the group afterwards should not be affected. That would just seem strange.

Imagine a group of four people standing together. A mage casts a sleep spell with T:Group, D:Sun on them. They fall asleep. Another person standing some distance off see them crumple down on the ground, and goes to examine them, thereby potentially becoming part of the group. Should he then also be affected by the spell and fall asleep? I don't think so.

For T:Room and similar the situation is a bit different, because while the contents of the room may change, the room itself will usually remain static throughout the duration of a spell. (But if someone were to tear down all the walls of a room, I could see the spell terminating from that.)

I am a bit unsure on T:Individual.
Assume an individual has had an invisibility spell cast on him. He and his clothes are now invisible.
He takes off his hat and throws it away. Does the hat remain invisible, or does it become visible?
He picks up another hat from a nearby table and puts it on. Does this hat become invisible, or will it remain visible, apparently floating in the air?

The answers I think I would like to have is that the thrown-away hat becomes visible once it is no longer worn or carried by the invisible person, while picked-up hat becomes invisible once the invisible man puts it on. This feels most in line with how invisibility typically works in myth and stories.

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17

Extra question - how does all this interact with magic resistance?

Let's suppose my hat is actually a Faerie, with 10 Might.

I cast my dynamic Invisibility spell in a Magic Aura 4, with a total of 7 + 4 = 11 penetration. My Faerie hat has 10 + 4/2 = 12 Magic Resistance, so it isn't affected by the spell, but I like my hat so I bring it along anyway.

I go somewhere where there is no aura, so my Faerie hat now has a Magic Resistance of 10. Historically I would have considered this to be irrelevant - I cast the spell once earlier, so there's no new test being done. Does the spell being dynamic in any of itself change anything?

I put my hat down and walk away from it, then walk back and pick it up again. Does the Faerie hat's magic resistance get tested again?

I wasn't looking at the hat when I was walking away from it, and when I turn around there are two apparently identical hats - both Might 10 Faeries. Do they behave differently when I pick them up depending on which was the original hat?

What is my penetration when I pick them up? Is it still 11 (in which case my spell now penetrates), or is it also dynamic and the fact that I am no longer in a Magic aura reduced it to 10?

If my penetration is also dynamic, repeat the tests in a divine aura of strength 4 - my penetration is now -5, but the Faerie's Magic Resistance is now -6.

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(As David reminded us, T:Group is static by RAW. So that issue is solved for me.)

You'd have the same issues if the hat Faerie was in a Room whose aura varied over time.
OTOH, if "wearing a snake" is not part of T:Ind, then we have a difference vs T:Room. A Magical Thing hat and a Magical Animal mimicking a hat are the same in a Room but not on a Individual.

Nevertheless, IMHO you have to flush the effect out before rerolling.
An ongoing effect is not affected by Aura changes, right? For instance, casting Aegis at the heart of winter solstice gives you a permanent boost even if the aura drops during the year.
OTOH, it will affect the Faerie MR on reroll.

19

As I am dwelling in the complexity of the Dynamic/group spell interaction, I have more questions.

The spell is cast on 8 grogs, clearly identified as a group, the spell has a duration of Sun (no really relevant - just long enough to have several events happening).
Established behaviour: The group disperses, thus putting the effect on hold. If the group reforms, the spell resumes its effects. Then another grog join the rank, so benefit as well of the effect (as established in a previous discussion on this thread).

First case: The group disbands again, a grog comes back with 5 other grogs, does the spell resume and affect 5 new targets ? How many of the original group needs to be present to apply the effect on other grogs ? Two (the minimum for a Group, since otherwise it is individual) ?

Second case: Since a group is mobile, if the inital group scatters in four groups of 2, can each of these sub groups forms its own group and have the effect resume ? Do they need to be within range of the caster for the effect to resume ?

Based on this set of questions, I would suggest that when a dynamic spell is cast on a Group, the effect only fade and resume on the initial participants, otherwise, some weird effects, hard to track would happen.

Other question: how does magic detection work ?
Especially on a member of a group that left the group - would he be positive to active or lingering magic, or a different type ?
If the whole group disband, there is no more apparent effect. But if the group reform, the effect resumes, so there must be a lingering trace of magic while they are disbanded, otherwise how the magic would resume ? And if there is a lingering trace of magic once a whole group disband, then there should be one on the member that temporarily left the group.
Does this trace last as long as the spell last ?

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20

I was thinking of the hat as being part of the Individual Target rather than a Group. Admittedly I can see being part of the Individual target being questionable if it is a Faerie rather than a normal hat, but you can substitute "has had Blessing used on it to give the hat divine magic resistance" for "is a Faerie" (and switch around the auras a bit) to get the same basic question set.