Is there a way to make a spell hard to dispel?

I was looking at making a ward, but it seems... trivial to dispel pretty much anything if the hermetic mage has a few days. Based on the Perdo Vim guideline

General: Dispel effects of a specific type with a level less than or equal to the level + 4 magnitudes of the Vim spell + a stress die (no botch).

a trivial to fatigue spont lv 5 spell can dispel a 25 + stress die. Assuming my statistics calculations are correct, that means that you auto dispell any lv 25 spells, dispelling a lv 30 is very likely (50% per cat) and lv 35 happens 6.9% of the time. lv 40 happening 3.8% of the time, and you don't pass below a 1% chance until lv 50. if you spent 8 hours casting it every 2 minutes you have a better than 90 percent chance of dispelling a lv 45 effect. boring, but still faster than spell creation.

First thing i looked at was rego vim but the closest in the core book

General: Sustain or suppress a spell cast by another with level less than or equal to half the (level + 5 magnitudes) of the Vim spell

but that doesn't seem quite what im looking for, and even so, couldn't they just do it twice, first targeting the rego vim ward then the inner spell?

Is there a way to make these theoretical wards more than a day's worth of waiting for the mage to get a lucky roll, other than traps or adding more active defenses?

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I might be mistaken, but the Base level does not include any range/target/duration parameter, so it will impact the final level of the spell.

To affect your own spell, you need a range of Touch (+1 magnitude), but to affect anybody else spell, you need a range of Voice (+2 magnitude). So a mage need to spont' a level 15 to dispel a level 25: the base effect is 5 +2 magnitude for Voice for a final level of 15. A lot trickier for a non-specialist, even with fatigue.
Other parameters are Ind (= one spell, so +0 magnitude modifier), and Duration is Inst. (also +0 modifier).

This guideline also mentions "a specific type of magic", so the mage must know what type of magic it is either through InVi or by inferring after observation what it could be (either watching casting of the spell and succeeding a MT roll, or because the effect is obvious, like Wall of Thorn).

IIRC, that particular guideline is later elaborated upon further (In Houses of Hermes: Societas, Pralixian subchapter). Specifically, you can only use that guideline for a specific sort of magic and only if you are very familiar with that system of magic.

Of course, this means you can use it for most Hermetic stuff more or less easily, barring certain stuff like Enchantments, Familiar Bonds (and Rituals, I think?) which would require ritual verison of Disenchantment to dispel. Anything else though, is gonna be more difficult.

The exact requirements are left to DM to interpret, but say that you want to dispel a Gruagachan Cursing spell. To be considered familiar with it, you'd need to have either examined it with Comprehend Magic, a Magic Lore score of 5, or Area Lore: Highlands of 2. Or had a chance to examine their enchantments as a lab activity.

Otherwise, if you are not sufficiently familiar with the type of magic you are trying to dispel, you need to use the following guideline:

Dispel any magical effect with a level less than or equal to half the (level + 4 magnitudes) of the Vim spell + a stress die (no botch).

Much less trivial, I'm sure we can agree.

Not quite correct, IMHO. You can affect your own spells in the same way as you target any magic.

Since it is stated on ArM5 p.157 (in Vim Spells) that "If the target is an object or person, the Vim spell will affect any suitable magic affecting that person, not just one spell." the result is that you can target yourself at R:Per to affect any suitable magic.

If you can a spell on someone or something else, you will need at least R:Touch to affect that spell. If the target is uncooperative, out of reach or other cannot be touch, then you will have to resort to R:Voice or more.

This appears to be the case for MuVi - it cannot be automatically generalized to PeVi (ie, dispelling).

Yes! My mistake, I was mixing up MuVi.

I disagree, actually :slight_smile:

"Well, well. We have taken care of that foul warlock, my lord. Yes, as promised. Meaning that the bounty ... uh, what? We must first remove his curse on you? To your virility? Let me see..."

"Ahh, a curse indeed. Still, it's only a tenth magnitude effect. Even my young apprentice here can take care of it. We are after all magi of the line of Apromor, masters of destruction..."

The earl goes deadly pale as his gaze falls onto his own groin.

"... PRECISE destruction, my lord. Of foul magics and magicians; no need to worry. It will just take some time. You'll need to devote to the ... therapy two hours in the morning, and two in the evening, in a quiet place with my apprentice. A day or two perhaps; almost certainly by the time I am back, in a week from now."

"Now lass, listen well. You are well-trained in the Art of destruction - enough to teach it to your own apprentice [Perdo 5+3]. Your knowledge of the Art of magic is adequate [Vim 0]. And you are full of youthful vitality [Sta+2]. Find a place with no supernatural interfence [No Aura]; here I perceive none. Firm Voice, bold gestures, no more is necessary - dignity! Above all, do not push yourself beyond your limits [non-fatiguing spontaneous magic]. Just keep at it, slow and steady. Two hours in the morning, two in the evening. Each session is a coin-toss: heads you dispel the curse, tails ..."

"NO, MY LORD. No need to worry. Your mistrust of us is just a side-effect of our Gift for magic. Now, lass, what was I saying? Tails, you try again. No, no fancy ceremonies. I know, you are unfamiliar with gruagach curses; no need to delve into that. Just use a broad-base dispel [Dispel any magical effect of level up to half (the effect level +4 magnitudes) + stress die.]."

"Very well, my lord. I'll be back in a week. Waste no time, start now. And treat my apprentice well - she's very partial to cinnamon pastries - or you'll regret it!"

The wizard disappears in a puff of smoke.



"I need to touch you, my lord. No, not THERE. Your shoulder is more than adequate. And you can get your robe back on. No, I can be just as PRECISE without seeing it - in fact, my concentration will be better. Sigh."

Ok, now the ugly, utterly un-mythical math of mechanics.
The apprentice has a casting score for Perdo Vim magic of 5+3 (Puissant Perdo) + 0 Vim + 2 Stamina + 0 Aura = 10. So she can manage Level 10/5=2 effects with non-fatiguing spontaneous magic. She casts a Base 1 + 1 Touch dispel over and over. She has to match the level 50 of the curse with a stress die + (1+4)/2. In other words, she needs to roll 48 or more on a stress die: that can be achieved by rolling three 1s in a row, followed by 6,7,8,9,0, or by an additional 1 and then any number except 2. So the probability of doing so on any single casting is 0.059%. The probability of not succeeding over 1200 castings (120 minutes of roughly 10 castings per minute) is then (1-0.00059)^1200, or slightly less than 49.3%. The probability of not succeeding over 14 two-hour sessions is less than 0.005%, i.e. less than one in twenty thousand.

EDIT - just to be perfectly clear. This is obviously a situation in which game mechanics produce a result running contrary to what one would expect. Most seasoned players of Ars Magica would probably agree that, in the ArM5 setting, an apprentice with a few seasons of training should not be expected to dispel over a day or two a 10th magnitude curse - particularly one from a tradition she's not familiar with.

But this is exactly the problem that the OP was highlighting. The rules do make it too easy (compared to "setting expectations") to dispel magical effects if the caster has ample time. I was simply objecting to Kodlak's suggestion that this ease stemmed from somewhat incorrect assumptions in the OP. The assumptions may have been incorrect, but the general problem is there. Removing the "+stress die" from the dispelling guidelines would go quite some way to ameliorating it.


There's a very good rule that appears in a good number of games, the first one i encountered it plainly stated was in was burning wheel, as follows:

Let It Ride

One of the most important aspects of ability tests in game play in Burning Wheel is the Let It Ride rule: A player shall test once against an obstacle and shall not roll again until conditions legitimately and drastically change. Neither GM nor player can call for a retest unless those conditions change.

Ars magic (and almost every other dice based rpg) is much improved with the addition of this rule


The "rule" (more of a general principle) sounds great in theory, but it suffers from a great flaw: ambiguity. It's not clear what "legitimately and drastically change" means, and in fact, BW books generally have to spend many words to clarify when it's applicable and when it's not. And from my experience GMs (BW's Storyguides) and players often end up disagreeing anyways.

Can you cast and recast a dispelling in the hopes that it will overcome a curse?
Can you cast and recast a mastered spell at R:Arc hoping for a casting total yielding sufficient penetration?
Can you cast and recast a mastered Pilum of Fire at a Dragon hoping for a casting total yielding sufficient penetration?
You may be saying "no" to the first, but the slope to the last (to which I'd assume you'd say "yes") is very slippery.

Ars Magica 5th edition still uses dice mechanics from 1st edition. This is good, because it maintains the feeling of the "same game" and keeps aficionados happy. But they are mechanics that do not handle too well repeated attempts, because you can get really high totals, and the game's mechanical infrastructure does not lend itself to limiting re-rolls in a clear way. By the way, I think this is in general one of the really big problems of game-engine design. Some systems do handle it slightly better than ArM5 (it helps to make sure that "when there's a chance of extraordinary success, there's a chance of catastrophic failure too"), but it plagues to some extent even diceless systems such as Amber.

That is a great example of roll-playing, which to me constitues bad roleplaying. I'd just tell that player it won't work, and leave it at that. After all, the characters don't know the statistical analysis of the game rules.

If the player persists, then after 10 or 20 rolls I'll have the character lose a Confidence Point due to the repeated failures. As a warning. After that, if he keeps persisting, I'll state that further rolls will be Stress with a chance of botching.

BTW, great storytelling by you, ezzelino. :rofl:


While I generally like the one attempt rule, it is an addition not RAW. And I can see a very good argument for none of it applying in this case: magi are magic researchers with labs, theories, repeated and reproducible experiments, along with all the math they need for this. magi should know about the random factor, have a rough idea of the distribution, and thus be able to take advantage of it.


I think you take a lot for granted about what magis know about chance and probability. Look up Timeline of probability and statistics - Wikipedia . You'll find there is, in fact, nothing published in Latin prior to gamestart about statistics and probability, and even while there is some obscure arabic texts about statistics, even they didn't delve into probability maths yet. The first latin text about analysing dice probability is from the 13th century, but likely posterior to game start since the author most likely to have written it is born in 1201. Even that text wouldn't yield much insight, because the magi are not really rolling dices. They probably have an inkling of what they can pull off, spontaneously speaking "2nd magnitude, about half the time", but that's about it. I don't think anyone has a really good explanation for rolling a 40 on a stress dice.

Consider also that Ars Magicka doesn't have any art called Entropy, unlike a certain game which had a similar background in terms of writer. If magi had a really good understanding of how luck works, they probably would have an art to manipulate it.


Negotiation of cases that cannot be disambiguated by a rulebook is an inherent part of ttrpgs, this is not a real problem in my mind.

Personally, I say no to all of them.
I'll usually allow a handful of tries but at a certain point you're just stagnating the game and should find a more interesting solution. Definitely not 2hrs a day for 2 weeks lmao.

I think I agree with this, you've described a series of examples where there's no downside for failure and can roll dice repeatedly, personally id be much happier if you just rolled once and could take something like a devils bargain from blades in the dark, because consequences are what keep games interesting, and rolling once and doing a brief exchange about what the consequences are keeps the game moving forward

Edit: to explain what I mean, this would be something like, yeah, you pulled enough penetration to harm the dragon, but it took you 4 hrs and your repeated use of the arcane connection has backfired and the dragon knows your location. Or yeah you dispelled the curse, but youre exhausted(long term fatigue) and repeatedly casting PeVi has neutralized your ability to cast magic for 2 days. Scaling by how high of a roll you'd need to get obviosly


As for the specific dispel thing, we know you don't necessarily need special Area Lore or whatever. Certainly, you might need it. For example, if you want a spell to dispel Learned Magicians' Magicam effects, then you do need to know something new. But let's say you want a spell to dispel shape-changing magic, regardless of whether it's from a Folk Witch or a Hermetic magician or someone else. Then you need to have some familiarity with that. Well Hermetic magi do have a lot of that familiarity, so Magic Theory, Muto, etc. should suffice. We know such a specification allows use of the better dispelling guideline (HoH:S p.129). So if it's something Hermetic magic can do, you can probably always use the better dispelling guideline.

More directly to the OP, here is one idea. Master a circular ward against people for Resistance (unless you don't care about stopping yourself). Stick your other stuff inside such a circular ward. Now if your ward can penetrate them, they can't knock down the stuff it's protecting.


Oh. So, in your magical battles, you rule that if a Flambeau casts a Pilum of Fire at an enemy and it fails to Penetrate, then every further Pilum will automatically fail to Penetrate that enemy's MR (unless, say, boosted by vis etc.)?

That's definitely an interesting approach. At first sight I do like it.
But I have never, ever seen it in play.

I bolded these because your math is wrong.
To dispel a level 50 curse, you need to match it to Half the level of the (Level +4 magnitudes) of the Vim Spell + a stress die. And this is without the +1 Touch you need for Range.

So, you need half the (Level +3 magnitudes) to be higher or equal to the level 50 Curse.
50 = (Level + 3 magnitudes)/2
Or, in simpler terms, you need to reach 100 on your spell casting.

So your apprentice has no chance of successfully casting it, unless you're willing to have him gain way more Warping than he should, and at that point, your Magi is facing multiple high charges in my opinion.

I think the problem is not that my math is wrong, but that we are reading implicit parentheses in the guideline differently. Namely:
I read it as "beat the target with: (half (spell-level + 4 magnitudes)) + stress die."
You seem to read it as "beat the target with: half (spell-level + 4 magnitudes + stress die)."

I think your reading is incorrect, both because otherwise the text would be parenthesized differently (with the stress die inside the parentheses) and because in math multiplication has precedence over addition - so half of six plus four is seven, not five.

While the location of the parentheses is indeed vague in the guideline, it is also addressed in another two spots in core, and there is only one way to reconcile them:

Dispel any magical effect with a level less than or equal to half the (level + 4 magnitudes) of the Vim spell + a stress die (no botch). (guideline)

Let's say you want Wind of Mundane Silence (using this guideline) to dispel a level-X spell. We have:

  • Guideline, halving the roll as well: 0.5(spell level + roll) ≥ X. Multiply both sides by 2: spell level + roll ≥ 2X
  • Guideline, not halving the roll: 0.5(spell level) + roll ≥ X. Multiply both sides by 2: spell level + 2x roll ≥ 2X

Now look at what the spell says:

You can cancel the effects of any spell if, with this spell, you can double the level of the spell on a stress die + the level of your spell.

There is clearly no 2x the stress die there. This agrees with the first option and disagrees with the second.

And then we can look at either p.156 or the erratum for that page, where we find

a level of up to half (spell level - 5 + stress die).

This is also in agreement with Wind of Mundane Silence and the first reading of the guideline.

Therefore the correct interpretation is that the die roll gets halved in that guideline. Not obvious since you have to look in two of three places, but definitely not open to interpretation.

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I see. Good to know!
In that case, the apprentice will only have to roll ... 95 or higher on a stress die. She needs to roll four 1s in a row, followed by a 6,7,8,9,0, or by a fifth 1 and any number but 2. So she has a probability of 0.0059% of succeeding, instead of 0.059%.

It will take her 10 times longer, but it's by no means impossible. Instead of having a slightly better than 50% chance of "rolling a dispel" every 2 hours of work, she has it every 20.

If her pater increases the "therapy" to three hours in the morning, and three in the evening, she still has better than a 77% chance of succeeding by the end of the week. Make it eight hours a day for a tenday, and it's better than 96.1%. So the point made by the OP remains valid, in my opinion.

And how many Warping points will she get in that time?