Fast casting against another wizard in Ars Magica

One of those forum conversations that leads into a brief explanation of how the game mechanics resolve magic… The Mirror of Opposition spell reverses the effect of a spell, but not the target. So a spell to hurt a person might help them instead. It is a very interesting spell because it relies on so many of the meta-magic layers in Ars Magica, primarily around Muto Vim spells, but there are compounding questions in the details.

Pyrale wrote: Another question regarding spell manipulation : Supposing I see someone starts casting, and I decide to cast a mirror of opposition on his spell. Does my spell have to pierce the caster’s defenses ?

If not, do I have a window of opportunity if the spell has no time of travel, or can I only cast it on projectiles ?

My 2c which might be dodgy… I think you can cast it on anything, and the SG gets to decide what it does.

  • First you need to use the rules for identifying what Form the spell is, because Mirror of Opposition is different for each Form, but I guess you might know if the caster had previously been shooting away with missile spells and just assume you’re correct if your perception Check failed. The Perception check isn’t going to slow down the rest.
    … Perception + Awareness + roll vs. 15 – (effect mag). If the opposing caster has silent/subtle magic/deft magic it gets a lot harder.
  • Then if you are not cooperating with the other caster (fair assumption) you need to fast-cast the MoO:(form), as per p.159 of Ars about not being able to intercept the spell quickly enough. Its basically a -10 to casting roll with 2x extra botch dice, and you need the fast-cast Mastery option for the MoO spell.
  • Then your Penetration total for your casting roll (which includes that -10 mod) must beat the other caster’s Penetration total
    (i.e. spell CT + roll – Spell level + Pen ability vs same from the other guy).
  • The rules imply that you don’t need to penetrate the caster’s parma which is great, although if they were casting a spell with Range: Personal upon themselves I’d argue that you’d also need to penetrate their Parma for it to work too (?).
  • The caster must be in range of your MoO spell too (voice), unless you’ve got a funky version or using an Intangible Tunnel and an AC.
  • I don’t know what happens if they are fast-casting a mastered spell, but I think you still could fast cast to intercept and alter it (?).
  • You can’t alter Spont spells with MuVi which is a bugger but it makes sense why.

Easy! However…

  • If the first spell was fast-cast then the second magus can fast-cast one to defend/intercept, but it should come back to speed (point made here). Essentially the magic system seeks to avoid situations where magi just fast-cast-BLAST their way through all encounters.
  • As MoO and many other Muto Vim spells do not work against Spont magic, and also typically must penetrate against the target spell, and also usually only affect half their level, not many wizards are able to Spont cast Muto Vim spells in defence. It is possible, but very unlikely.



A thought on affecting spells with requisites, a meta-magic question for Ars Magica

An aside – How do requisites affect which spells can be affected by magic?

A question raised during the forum discussion asked if a Muto Vim effect could change a spell enough to make it no longer effected by a Perdo Vim form specific effect. e.g. A Sun duration Rego Terram effect is altered to a Rego Aquam effect at cast time – can a Perdo Vim/Terram spell affect it if it has “changed” the form it uses? Further could the same Perdo Vim spell affect only Terram spells, or can it also affect spells with a Terram Requisite?

I tend toward thinking a spell with a Tech and two Forms can be affected by either Form specific dispel effect. The unraveling affects part of the spells structure and it doesn’t really matter which form it unravels to make the spell loose it’s cohesion. This makes requisites a slight disadvantage, and implies that some part of the original spell is still there to be unraveled.

But I hold the same concept to other ways of affecting spells it also introduces an advantage to Mu effects affecting the Forms too. i.e. a Muto Vim Terram spell to alter Range up by 1 mag can be applied to any spell using Terram, either as the base form or a requisite. I don’t see adding breadth of application into Vim spells as unbalancing.


A floating book, all a wizard needs

An item of fancy and indulgence for those Magi who insist on looking the part and being most prepared. It might also make a good justification for a lab improvement item with a focus on texts or reading. This is a similar function to the Bookstand of Hespera (Covenants, pg 121) except it affects just a book rather than a place to write and work. More purposeful for reference and study instead of creation. It will also cause warping in the target books over a long period.

Bookmark for a Text at Hand  (ReHeAn 25) is a small plate which is touched to the desired text and allows the text to float as the caster desires.

Ready an Attentive Tome

Rego Herbam / Animal 15, R: Touch, D: Concentration, T: Individual

The targeted book, scroll, or text floats next to the caster and can be set in position via concentration.

(Base 5, +1 Touch, +1 Concentration)

(+5 Device maintains concentration, +5 for 24 uses per day)

With a final device level of ReHeAn 25 the devices are still cheap enough to be crafted by more junior magi, and may well be used as lab texts for an inexpensive boost to labs. The bookstand from covenants “adds two points to a specialisation in texts“, and has a slightly higher baseline although lower final level. This device is designed to that it can be used to direct many books at once, each sustained by the bookmark and controlled by the user’s concentration. It makes sense that it would offer a similar bonus and also have a more diverse application than a singular bookstand.

Rapid growth of a natural grove, room, or wall

This is a spell which rapidly grows a set of trees, cast on an existing seeds or saplings, allowing their branches to intertwine to the caster’s design. The intent is to cast upon many plants at once to imitate rooms, walkways, barriers, etc. Spells which do this are frequently high level as the smallest base effect is level 15, and from there the magnitudes stack quickly. A subtle caster may mark trees amongst a wider set with a sigil or paint so they can be easily identified as a Target: Group.

Although it would only be a note in the setting, the same spell could be used to guide the rapid growth of plants such as grape vines or fruit trees on farms in a manner which makes them easier to manage.

Growth of the Structured Grove

Creo Herbam / Rego 45, R: Touch, D: Sun, T: Group

The targeted seeds and saplings mature over the day duration to their adult size in an alignment and layout to suit the casters desire. Branches may be intertwined, leaves given favorable angles, and limited only to the broad fundamentals of their plant type.

(Base 15, +1 Touch, +2 Sun, +2 Group, +1 Rego sub-effect which dictates shape)

This spell is part of the free new spells compendium for Ars Magica.

More spells and items for lab improvement, p4

For November 2017 Ars Magica writing challenge – I’m doing one spell a day.

Warmth of the Cozy Solar

Creo Ignem 15, R: Touch, D: Concentration, T: Room

This room is provided a pleasant heat, granting the Superior Heating attribute to a lab (Cov p.114).

(Base 2 for warm to touch, +1 Touch, +2 Concentration, +2 Room)

Device effect total 14 (+1 for 2 Uses/day, +3 trigger: sunrise/sunset)

This spell is part of the free new spells compendium for Ars Magica.

More spells and items for lab improvement, p3

For November 2017 Ars Magica writing challenge – I’m doing one spell a day.

Touch of Daylight 

Creo Ignem 10, R: Touch, D: Concentration, T: Individual

The object touched shines like the sun on a cloudy day. If used often within a lab it grants the Superior Lighting attribute (Cov p.114) without the upkeep cost

(Base 4 for light of a cloudy day, +1 Touch, +1 Conc)

Device effect total 20 (+5 Device maintains concentration, +5 for 24 uses per day)

This spell is part of the free new spells compendium for Ars Magica.

More spells and items for lab improvement, p2

For November 2017 Ars Magica writing challenge – I’m doing one spell a day.

Insulation for the Dedicated Halls

Perdo Imagonem 25, R: Touch, D: Sun, T: Structure

This effect stops any sounds from entering or leaving the structure, granting the “Well Insulated” lab virtue (+1 Safety, +1 Aesthetics).

(Base 3 to remove sound, +1 Touch, +2 Sun, +3 Structure)

Device effect total 29 (2 uses per day +1, environmental trigger +3 = constant)

This spell is part of the free new spells compendium for Ars Magica.