5E Homebrew Spell Advice

Good day,

i am a neophyte story guide to Ars Magic 5e, and would like some advice please from those with more system mastery. A player in the group has brought me 3 spells he would like to create for his magus, and would like me to ok them. I feel like i dont yet have the system mastery to give him the yea or nay and would hope to wiser minds to parse them. They are as follows:

Spell Layer 1 (innermost)
Shield Of The Magus Lvl 30
Range: Touch
Duration: Sun
Target: Individual
Req: Perdo

This spell works similarly to a magus' Parma Magica. When a spell or ability must be resisted magically and the spell or ability is activated, it is the last line of defence. If the spell/ability does not penetrate this shield, the spell/ability has no effect on the target. If the spell/ability breaches the shield, it is at a level less the level of the shield. If breached, the shield will be at a strength of 1/5 the level of the breaching spell less from the original level of the shield. It is designed to be layered with other shield spells, other than itself.

Spell layer 2
Shield of Increasing Strength Lvl 30
Range: Touch
Duration: Sun
Target: Individual
Req: Creo, Perdo

If this shield is called upon to protect the magus against magic (spell, ability, etc) and the level of effect is lower or equal to the level of the shield, then 1/5th the level of effect is added to the shield and the shield then protects at that new level immediately. The maximum that the shield can be increased to is double the level of the original shield spell. If the shield is breached, all gains are lost, but the shield will go back to it's original strength immediately. If the shield is breached, the breaching spell's level is reduced by 1/2 the current level of the shield.

Spell Layer 3 (outermost)
Shield of Reflection Level 30
Range: Touch
Duration: Sun
Target: Individual
Req: Muto

If a spell is cast at this shield, and does not penetrate it, one of two things happen. If the actual spell level is half then that of the shield, it is reflected back at the caster of the spell and, because the spell is a creation of the original caster, it goes through the original caster's Parma Magica as if it was not there. If the spell level is higher than half the shield's level, but lower or equal to the shield's level, the spell deflects in a random direction (but away from the intended target). If the spell breaches the shield, it goes through unaffected. If breached, the shield is back at full strength immediately, as if it had never been breached.

Feedback is gratefully accepted.

The answer should be No for multiple reasons.

First they are not a properly designed spell that would allow you to judge their validity as written. Perhaps it was submitted and you did not post it, however it is a critical part for others to give you feed back. If you are wondering what I am talking about, it is the block at the end of every spell and effect in every book. It would include things like the TeFo Base used, any modifiers to that base, R/D/T modifiers, Requisite modifiers, and additional modifiers.

Second there is no Art Te/Fo base which functions as a Parma Magica. In other words, Hermetic Magic currently has no means to achieve what he is attempting. It can not be done without extensive Original Research (HoH:TL, p. 26), most likely at a Hermetic Breakthrough for each spell base if it is even possible (I would strongly suggest none of them be possible as spells for most games).

Third there is already an example set of Original Research modifiers to Parma Magica which can achieve much of the goal (HoH:TL, p. 31). These are a modifier to Parma Magica rather than spells which makes them easier to research. For most games, this would be the closest to what the player wishes that would be allowed.

I hope I am not coming across as too harsh. If both of you are new then it is a learning experience.


One important part of the background lore of Ars Magica is that so far nobody has managed to create a spell that gives you Magic Resistance. While such a thing is not impossible, it would probably require half a lifetime of research to make it happen - in the best of cases.
So I for one would just bluntly say no to those spells, or any other spell giving a mage anything like the Parma Magica.


I would say no to all three. If you are new-ish, I would suggest limiting the selection of spells to core book plus possibly the House books and leaving it at that until you and the player are more comfortable with the system.

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Troy and ErikT are both right.

To complement what Troy said, my advice is to look at how spells are designed in the base book, to expect players to use that template when creating a new spell, and to use that template when posting on the forum. Something like this:

Technique Form (Level)
Spell Name
Req: If applicable


(Base X, +X Range (if applicable), +X D (if applicable), +X T (if applicable), +X any requisite or other factor for complexity such as fancy effect, unnatural, complexity, etc.)

Why is this important? Because it will be very hard on you as a storyteller to assess a spell without looking up the guidelines. Chances are, if you can't easily pinpoint the guideline the player is using... maybe he isn't using the guidelines and is just randomnly creating an effect and assigning a spell level. I believe this is the case here. Let me apply that template to the provided spells to help you see the mistakes:

Unknown Technique (Rego? Muto?) Vim (Obviously intended) 30
Shield Of The Magus
R: Touch, D: Sun, T: Ind
Req: Perdo

This spell works similarly to a magus' Parma Magica. When a spell or ability must be resisted magically and the spell or ability is activated, it is the last line of defence. If the spell/ability does not penetrate this shield, the spell/ability has no effect on the target. If the spell/ability breaches the shield, it is at a level less the level of the shield. If breached, the shield will be at a strength of 1/5 the level of the breaching spell less from the original level of the shield. It is designed to be layered with other shield spells, other than itself.

(Base 10 inferred from reverse engineering spell level, +1 Touch, +2 Sun, +1 Perdo)

If this was a muto vim spell, they would come with all sorts of restriction, and would not function as a static magic resistance on a target. Therefore, this is not Muto Vim. Under Rego Vim, the closest thing we can find to magic resistance are wards (they affect creatures, not spells, so this spell does not match the guidelines) and effects to temporarily suppress a spell. This does not temporarily suppress a spell, so this wouldn't work under Rego Vim. Under Perdo, on the other hand, you have effects to weaken a spell or to dispel it. This looks like a spell to weaken a magical effect, so this kind of effect could fall under Perdo Vim (e.g. Perdo could be the technique here, rather than a requisite). Let's say you're trying to help your player. Once you figured out the effect he wants to build really is under Perdo Vim, you can try and rebuild the spell with Perdo Vim as a technique rather than a requisite on a spell that doesn't have a clear technique. Rebuilt as a PeVi 30 spell, without the +1 complexity from the requisite, you would have a base effect level of 15:

Perdo Vim 30
Shield Of The Magus
R: Touch, D: Sun, T: Ind

(Base 15 inferred from reverse engineering spell level, +1 Touch, +2 Sun)

In regards to dispel, there are two guidelines, one specific to a form (more powerful), and a more general dispel (weaker). This is the guideline you would want to look at:
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).

Base 15 + 4 magnitudes = 35. This gives: "Dispel any magical effect with a level less than or equal to 17 + a stress die (no botch)."

What about the duration? Does that mean any spell of level 17 + stress die that is incoming on the target would be dispelled? No. First, Perdo Vim must target an existing effect. This is problematic, because if the spell does "You die", you have to perdo vim during the casting, because by the time you get to dispel, it's too late. Perdo Vim doesn't simply wait for an effect like the described shield. Second, the effect of a Perdo spell with a duration is typically to prevent what was destroyed from being healed, from filling the destroyed area, etc. So I would say that a dispel with a duration would remove an existing effect and prevent a dispelled effect from being recast. This is very, very far from a general magic resistance, which isn't possible even under Hermetic magic except through Parma Magica and Aegis of the Hearth, both of which are very specific effects that cannot be easily modified short of a hermetic breakthrough research requiring probably decades of research.

As to effects #2 and 3, I will not look at them in detail, except to say that I believe your player hasn't followed the spell guidelines anymore than he did for effect #1. For the moment, just trust me on this and say no.

As a new storyguide, I'm assuming your players are equally new to the game, and my advice would be to tell your players not to come to you with a complete spell until they have mastered the guidelines. It will be easier on you and on them. Instead, when your player wants to design something, I would recommend doing a step by step with them.

  1. Ask them to identify the art & technique combination they want to use;
  2. Ask them to pick a guideline from the tables in the base book. If what they want isn't in a guideline, ask them to describe what it is they want to do. See if it matches a different technique or form combination. If you can't find a technique and form combination guideline that works as a base effect... assume that what they want to do doesn't work, and have them follow a different line of research. You don't want to get into original research for a neophyte game.
  3. Once you've identified the technique and form and base effect, read the text in the box of the guidelines to see any other things that apply. For example, Muto Vim comes with a lot of restrictions of what it can and cannot do. Intellego Vim expends the base guidelines to explain how that can apply to creatures and items, and explains that most spells detecting magic also incidentally tend to detect vis. These should be factored into helping you build the spell.
  4. Have them pick Range, Duration and Target. Size can be factored by looking up what is a base individual under the art description. Calculate the final level of the spell. At this point, your players may want to reconsider some decisions based on their lab or casting total.
  5. Once you've agreed on the spell parameters, you need to figure out what the spell actually does mechanically. Does it look plausible? If in doubt, look at existing spells.

Once you're confident that your player has a good grasp of how spell design works, and that you do too, as a storyteller, go back to the start of my post, and start asking for templates that are fully completed. If they can't provide a complete template for you to assess, assume they are not autonomous yet, and stick to the step by step.

Also, welcome to the forum. Make yourself at home.


I remember a ArM5 Spell Guidelines file which covered all the guidelines in the Core book. It was similar to the ArM5 Supplemental Spell Guidelines file still available from Atlas (here).

While I will not be sharing one without permission from Atlas (since they might feel it is sharing of their work), building your own from the core book might be very useful. You could fit all of the RTD and TeFo Bases onto ~10 pages and print it out, giving you a guide to hand to your players when they attempt to build a spell.

Thank you everyone for your insightful advice and critique. This is the first Ars Magica game i am story guiding and while i have been a games master before for other systems, system mastery always takes me longer than i would like, and Ars Magica is very different from other systems i have run.


I'd second the recommendation to only use existing spells from the books when creating new characters - especially for a new player / storyguide.

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I might be inclined to allow existing spells with tweaked parameters, depending on how confident you're feeling - "it's like Pilum of Fire but at Sight range rather than Voice range. I call it Arrow of Fire."


I agree with everything above.

Also, for your first game as SG, I would suggest taking that player to one quiet side and have a serious talk with him, because he seems to be going to play a Vim expert, and that's not something I'd suggest both of you to play until you are both quite confident with the system.

Also he seems to be going to ask for 90 spell levels just to boost his magic resistance. If he is the average magus after apprenticeship, that's 75% of the spell levels he gets. The remaining 25% would be so thin he seems to be going to be doing what, resisting magic all the time!? Which, anyway, is what Parma is for. Suggest him to focus on other arts and spells and style of magus, and if he is paranoid about magic resistance tell him to get Puissant Parma or Affinity with Parma. And of course don't start throwing might 50 creatures, 150 years old archmages and faerie queens to them right on the first story.


I agree with all the advisc above, and the comment of take it as a learning experience.

Those spells would break the game. That magi would be near impossible to hurt with spells, meaning if you ever wanted to be able to have a chance to touch him with magic, any other magi nearby is devestated.

As mentioned by another poster, he also would be painfully boring, as what could they do apart from be magic proof. Only 30 levels of spells left.

Yes. I once shared such a document and was asked to desist.

To rule on spells, I would strongly suggest also to prepare in your storyguide screen / notes a table summarizing the various RDTs effect on level:

Also, read carefully the rules on Size and magic (Target). They are a bit confusing. My summary:

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