A tricky MR question for ArM

I saw a tricky Magic Resistance question for ArM today, and I find it a frustrating demonstration of the MR rules, and a potentially exploitable rule.

RacconMask wrote – How does this react with Target:Part? If I take (for example) a javelin or spear, and cast a Target: part spell to control the butt of the spear’s haft to attack flawlessly with Rego… does that get magic resistance when the un-controlled tip stabs in? Thinking here of an ‘invisible swordsman’ ReFo spell that only controls the hilt of a weapon.

Grumble. It is a great idea as it demonstrates again how MR in ArM can be complicated. Truthfully it is no different from enchancing a soldier with a spell to increase their toughness, and insisting that they use normal weapons. Which is to say the players at the table need to understand a simple rule – When a rule is exploitable it can be used by everyone, and the GM has far more resources. Do you really want your enemies to react in the same way?

As long as the exploit is applies consistently and it feels congruent in the story, let the players exploit. Then hit them with it.

This is the same for Parma Magica burning spells. They look great on paper, and are exceptionally dangerous, but they also will likley impact the players far more once the NPCs adapt.

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Should MR affect Wings of Soaring Wind?

Whilst googling around for Ars Magica material I came across the RPG Stack Exchange pages, and an interesting question was asked – Does Wings of Soaring Wind need to penetrate the caster’s Parma?

Go over an have a read; the short answer is yes. There is no elegant work around that I can think of except the group of players agreeing to hand wave the issue due to how cool the spell is. That said, some left field options and discussion carries on below. Continue reading

Testing for Magic Resistence

Events in an Ars game yesterday had me thinking of ways to find out if an opponent has MR. Trying to “kill something with fire” will always tell you but it has drawbacks. What about a light “touch” spell?

A few of the expansion books added “forceless casting” which allows a spell to work but have zero penetration, in a manner similar to most magical devices. Useful for casting where you think a Hermetic wizard might be within your targeted area, but the wizard casting the spell also needs to remember to use it. Oft times having a little extra force behind a spell is useful.

Within the game scenario the potential target is probably without MR but might be a special creature type. It is very unlikely to be an Order of Hermes magus. In this case I may not want my character to cast forcelessly, I want the effect to penetrate any MR it might have, so I get a sense that it either has none or not much. If the spell is low level enough it could be cast a few times to test both those scenarios.

My quick requirements for the spell are: target at Range: Sight, very hard for observers to notice, and especially easy to cast. The lower the spell effect the better.

Any spell Form guideline of level 1 is useful as it can be extended to suit, so I picked Muto Imagonem. Imagonem is very handy as it can affect any substance without an additional casting requisite. So the spell below can be cast on objects, animals, humans, or almost anything really.

Subtlety Walk Between Sunshine and Shade

Muto Imagonem 4, R: Sight, D: Momentary, T: Individual

The hue of the target’s image subtly shifts, to either slightly lighter or duller in a manner similar to cloud passing over an object on a sunny day, or the reverse. The caster may choose which effect at cast time.

(Base 1, +3 Sight)

The effect is simple and subtle. Other observers may be able to notice the effect, although it will be exceedingly difficult unless warned in advance. A creature with magical resistance will always “feel” the effect if they successfully repel it, but with this spell others won’t really notice it.

More custom spells can be found in the New Spells for Ars Magica page.

How does MR and Penetration work in Ars Magica?

I swear on all things unholy that the descriptions in Ars Magica 5th edition on how Magic Resistance (MR) and Penetration work are confusing. As a roleplayer’s PSA here is my breakdown of how it works, with a worked example that explores some of the edge cases you’ll encounter.

(I’ve checked with the gurus in the Ars Magica official forums, so the worked example below should be accurate.)

So how does MR and Penetration work in Ars Magica?

The simple explanation is that the penetration total for a spell must be higher than the target’s magic resistance. If they have no MR, then the spell effects are resolved as normal. So the Penetration total must exceed the MR.

As a basic principal the more raw power the Magus has to cast the spell the better, however that power is used for the generation of the spell effect and also for determining if it can pierce the Magic Resistance of the target. Essentially the more power the Magus uses in generating the spell, the less power they have to defeat any MR they might encounter.

That might seem odd, but it makes sense when you consider that most mundane targets (most normal humans) have no magic resistance at all. So against those targets the caster can opt to use their best very powerful spell (such as an instant death spell) instead of a far weaker spell that might just hurt or paralyse the target. The lesser powered spell might harm a creature with MR, as more of the remaining potential energy is being used to penetrate the creature’s resistance.

However almost all of the supernatural creatures, Magi, and some holy men do have magic resistance from various sources, and their MR must be overcome before considering the effect the spell might have. Thus the Ars Magica rules were updated in 5th edition to demonstrate that MR is valuable and something that Magi must consider when fighting with magical enemies.

So the penetration is the remainder when spell’s power level is subtracted from the power the magus generates. This means that sometimes the penetration value (the remainder) is less the magic resistance of the target, and therefore the spell is repelled. Sometimes the remainder is negative, which means that while the spell was cast successfully, the spell could only affect creates that have no magic resistance at all. i.e. It would only affect mundanes.

Continue reading