Shrinking or decreasing size spell


I'm new with Ars Magica, but i searched all books and past 3 hours this forum, looking for spell to decrease mage size. I think it should be MuCo, but I cant find table/spell who show me how spell lvl change on size. Base would be 3, but if i want to become -12 size(normal size 0) or -18, how negative levels effect spell level?

ArM 5 Main Rules: p 132, Muto Corpus guideline - Level 3: "Utterly change the ... size of a person."

So, Level 3, +2 Sun, a level 5 spell to shrink someone at least to -1.

...Now that I look at this, though, I wonder how "utterly" you can change a person's size at that base level? -1 Size per magnitude? Can you just shrink someone to Size -7 from a base 3? Surely not - you could make someone a giant. I see why you're looking for a chart. I'd think it should be -1 Size per magnitude.

I seem to recall a discussion of size-changing somewhere in the ArM5 books.

Edit: There is a discussion of Size in HOH: Mystery Cults, p. 39, but it is in relation to various animal sizes.

ArM 5 : p. 131
Preternatural Growth and Shrinking, MuCo base 3 allows a reduction in size by up to 2 points.

I would tend to allow 2 points of size reduction per magnitude.

This has never been clarified in any book of the 5th edition game line (in 4th edition, it was in The Mysteries, but it's not quite compatible with 5th edition -- among other things because in 4th edition Arts tended to run higher, and spells above level 50 were not necessarily Rituals).

MoH, p.49., has a spell to grow the target, and it uses as a guideline the idea that you need enough size modifiers to make sure that the magic can affect the "end result". Since each +1 magnitude multiplies the mass of what you can affect by 10, which corresponds to a +3 increase in size, with the basic effect you can grow a target to size +1 (which is still a basic Corpus Individual); with an extra magnitude you can grow him to +4; with two extra magnitudes to +7; and so on.

This of course in no way helps with shrinking -- in theory if this were the only limitation you could shrink the target to an arbitrarily small size with just the basic effect (plus magnitudes if the target started out large). Now, if you look at RoP:F, it tells you Faerie powers work exactly like this -- an arbitrary shrinking for just the basic effect.

My troupe has long (since the corebook came out, essentially) been using the following House Rule, which seems in line with what Achlys suggested, but is not compatible with what MoH provides (it's more restrictive). The basic effect provides either +1 growth, or up to -2 shrinking, as per Preternatural Growth and shrinking. Each additional +1 or -2 adds a magnitude. So, to shrink by 12 sizes would require Base 3, +5 magnitudes, i.e. Base 20. To shrink by 18 sizes would require Base 3, +8 magnitudes, i.e. Base 35. After many years of gaming I find it a bit highish for my tastes, but ...

And now I have a desire for a mage NPC who specializes in growth and shrinking applications. There are several highly applicable SF plots for this.

I just found this part about Faerie shrinking, so if I build magic character human, and want to use this focus power for going from 0 to -18 i will need that power to be 35lvl, or it can be lower? Because there is "This can simulate the effect of any size-changing spell of level 25 of less." And then i would need power to return to go normal, yes?

There was one, but he may have been cut after playtesting.
I remember sending a lot of time figuring out how changing sizes worked. And I'm not terribly happy with what I found.

In the past I've kept the base 3 for the initial shrinking effect and then said each additional mag reduces size score by 3.
It kind of works:

As already explained above, there are no rules for large Size changes. I too follow the extra -2 Size per extra magnitude house rule. To be more exact, here are my house rules on this:

Edit: You might also want to decide what are the game-stats for tiny magi. And what does it do for armor (Protection, Load)? And for weapons (including natural weapons)? There are, again, no really clear rules on this. If you want to keep things simple, I suggest you follow the following rule: calculate everything as for the normal character, including Load etc., and then apply the changes:

  • Increasing Size by +1 adds +2 to Strength and -1 to Quickness, and increases the damage range of each wound level
  • Decreasing Size has the opposite effect (with a minimum damage range of 1).
  • An exception is Size -1 and +1 for humans, that doesn't change the Characteristics.

If you want to be more "realistic", then things can get more ... complicated. I personally find it unacceptable for a huge sword to dish out as much damage as a normal-sized sword, for example, but calculating how to change things makes changing Size very cumbersome and you will never get really-good results. I might suggest something like the following:

  • in addition to the above, increasing Size adds +1 to Init, +1 to Damage and +0.5 to Attack [round down] of enlarged weapons (natural or artificial), and adds +2 to their Str requirement.
  • For every +1 Size, weapons triple their Load up to Load 5 and double it for each further increase (e.g. increasing a Lance, with Load 2, by +2 Size will increase its Load to 12: tripling to Load 6 for +1, then doubling to Load 12 for the other +1). This doesn't make perfect sense, but is fairly simple and seems to roughly work-out in the sense that it let giants be reasonably-Burdened by standard arms & armor.
  • Armor keeps its Protection, and adds +2 Load per +1 Size increase; it presumable doesn't become much thicker.

No, no! What the blurb in RoP:F is telling you is this: an effect that shrinks a human-like character (so Corpus, and initial size at most +1) to any specific size, no matter how small, is Base 3, plus magnitudes for RDT. So, to give such a faerie a power that allows it to become size -18 until the next sunrise or sunset would be Level 5 (more precisely MuCo Level 5, R:Per, D:Sun, T:Ind) obtained as Base 3, +2 Sun.

Note that the effect is to give you access to one specific reduction: shrinking to size -12 and to size -18 are different effects, and would require two different powers (or you may be able to put both in a single power by adding a magnitude, as in Preternatural Growth and Shrinking). This means that if you want your faerie to be able to assume any negative size, sometimes being large as a child, sometimes large as cat, sometimes large as a mouse, sometimes large as an ant etc. then your best choice is to take a Focus Power, that allows the faerie -- like with spontaneous magic -- any effect within a certain scope, up to a given maximum level. As we worked out above, for something that lasts up to a day and affects just the faerie, you only need a level 5 Focus Power, leaving you the remaining 20 levels provided by the VIrtue to spend as you wish.

As for Duration. In general, a power lasts its full duration, or until dispelled, and that's it!
So, if you took a non-focus power that turns the faerie to size -18 for D:Sun, it stays small until the next sunrise or sunset, or until something (including another power) dispels the effect.


I think shrinking by any set amount uses the basic guideline. (But remember that if the target starts off really big, extra magnitudes are needed to account for that size.)

I also think that it is reasonable to add a magnitude for flexibility to shrink any amount with a single spell.