What an interesting, original idea. The only thing to keep in mind that your giant growth spell still has to penetrate if you want to stomp/wrestle anything with Magic Resistance - so it it your best choice for the Mythic Blood spell?
A +1 bonus to Stamina would be better i think, big doesnt need to mean high stamina, although its hard to be big without being stronger, or movement gets very troublesome, so Str gets +2 per size level.
Or perhaps a direct bonus to soak at +1 per size level would be better still? I agree there should be some bonus for it from size.
Keep in mind that size also affects the levels at which the character takes different wounds. Increased size doesn't make the character less likely to take Light wounds, but does make it significantly less likely he will take Medium or Heavy wounds. I think you shouldn't increase Soak or Stamina unless another effect gives the character tougher skin or some kind of armor.
Which is precisely why we have been discussing this as a matter of becoming an actual ICE giant. as far as frosty themes go cant get any tougher or armoured than ICE (20,000 kilos worth to boot). 
I think we are set for the extra resistance to cold for the mythic blood effect. Now we are in effect working in the combat abilities of the magus 
Fighting as a giant has a strong appeal after all
Most people commenting seems to agree that a +6 size would give a +12 strength and -6 quickness, as per the beast guides. Also, the damage range increments would be affected (becoming larger).
Soak and armour is the point now.
Do you think a further spell would be needed here? IN fact, given the fact that I am a hermetic magus, as per the RAW a dragon or griffin would not be able to touch me if it does not break my parma magica, right? But Mark probably will never accept that 
so an increased soak spell would be welcome
The "problem" comes from the +5 soak being a base 25 effect. Quite massive really, specially when you have to add Sun/diameter and +2 size to the combination. Makes for prohibitive soak boosts really fast. And a meagre +7 soak or so in the end for a 12 meters tall creature using a level 45 spell. Sounds rather weird. More than ice it sounds like a bohemian crystal giant!
Cheers,
Xavi
I don’t think so. By the RAW, your Parma would certainly protect you from any Might based powers the creature tried to use, but it could still bite, claw, or stomp you normally. In order for it not to be able to touch you at all, you’d need to Ward against it.
I would argue yes, for the same reasons Mr. Dahl noted above.
I think the problem is that skin is not naturally resistant to physical attacks, and so making it hard as leather or metal while still preserving its mobility is magically very “difficultâ€. Plus, it prevents the MuCo specialist from shrugging off any attack while naked .
If you want to increase your soak, your best bet may be to wear lots of armor and then layer several spells of somewhat lower level, rather than one massive one. Bear’s Fortitude or similar, Doublet of Impenetrable Silk, something that makes your armor tougher, and the like.
well diamonds are called "ICE" in slang, so one spell for icey giant and second spell for Hardness of the Icey Gem, MuAq(Te) I believe.
The flambeau will have fun using you for optical refraction studies and spectacular light shows lol.
I formally petition for the covenant name to be changed to Psychadelica, after all we one weird mixture lol.
Hardness of the Icy Gem (MuAq(Te)30)
R: pers, D: sun. T: Ind
Turns a large ice surface (including a glass giant of up to size +6 
) tough, granting an armour level of +15 to soak against any source of damage.
Base4: change dirt so that it is highly unnatural (moving ice would qualify here)
+2 gemstone, +2 size (up to size +6 to affect up to a whole ice giant), +2 sun
The exact soak level is decided at random. +15 sounds about right. With the +2 stamina of my magus, it becomes a soak of +17 for the full ice giant. Sounds about right when stellatus has a soak of +20.
The overall combo requires 3 spells of level 25-30. One to turn into a giant. A second to make the giant tough and a third to summon a large ice weapon. or to make a small tree tough enough to be used as a weapon. Quite a bunch of spells really. Especially when you consider that they will need to be duplicated for a +3 size giant/ogre (the ones I will have to hunt down smaller quarry.
Xavi
Think I might have something similar in my repertoire
Concerning the names of ice mages:
I play a Flambeau Hoplite Maga named Friga Glacialis, and she's quite an ice specialist.
She was converted from 4th ed, where she had a spell that created an incredibly hard armour of icy scales. I dropped this in 5th ed, as we in my group felt the guidelines actually didn't support this effect as a (ralatively) low level spell. The complexity of having the armour still be somewhat flexible is too high.
But in theory one could make the armour as a curiass! Such a plate is simple, just one piece of shaped, hard and inflexible material...
The spell above is NOT creating a cduirass: it is tranforming the whole body of the ice giant so it becomes hard and impervious to damage. Hence it is a Muto spell, not a creo one.
What guidelines were you using, Ultraviolet?
Xavi
The spell is an interesting idea, but does seem to call for revision. +15 Soak is awfully, awfully high for a spell that’s only base 10 (4+2 for gemstone). For that matter, a base individual for a gemstone is one cubic inch, so you would need more magnitudes for size. Rather a lot more, in fact. Not to mention that, if your whole skin were changed to gemstone, you probably couldn’t move – which normally calls for “Complexity†magnitudes tacked on if you want to be able to do so.
For changing skin to be supernaturally tough, I personally wouldn’t go any higher than you can do with regular MuCo – those guidelines are, one presumes, there for a reason. Creating ice armor that’s supernaturally tough, on the other hand, is entirely possible and much more within the bounds of the rules. Armor is supposed to give a (relatively) big bonus to your soak, skin is not.
Looking thoroughly at the CrAq guidelines, lvl 4 is "Create Water in an Unnatural Shape". IMHO an armour of ice is at least unnatural, I'd perhaps make it even more unnatural and complex. So perhaps 1-2 (or more) magnitudes for complexity and hardness of ice, +1 for Touch and at least +1 for Diameter (or +2 for Sun), so at least lvl 20! Perhaps even as high as 30!
I see the problem with the flexibility of the armour. It's of no use if it's a rigid block of ice, however high Soak it'd give.
Either a simple curiass could work, but should still need some straps etc. A Lorica Segmenta could also work, or even a Scale Mail. Perhaps if the spell is defined as creating the armour plates/scales on a cloth backing. So as long as you wear some appropriate cloth vest or shirt, the spell can create icy scales to stick to it, and move as would they have done with a steel scale armour.
How about hardness? Hard packed, deep-frozen ice can be very, very hard! As hard as steel, or harder? I don't think the ice should and could be supernaturally hard. Also, this could be overpowered and unbalancing.
Since my Maga dropped this ice armour, she made do with a "Doublet of Impenetrable Silk". Perhaps this trademark icy armour should have a renaisance?
I did do that chart, yes, but for 4th edition. It was based on an exponential extrapolation of the known animals at different sizes, because 4e had no rule to Size.
I did a 5th edition one as well, which can be found in HoH:MC. This is based on weight rather than dimension, and based on the nice firm footing that Size +3 = mass x 10. An orca is now Size +5, and a humpbacked whale is Size +9 (=64 tons, although Size +9 goes up to about 77 tons).
This is based at a human being Size 0 and 154lb (=70kg) average. Thus Size +3 is 1540lb, Size +6 is 15400lb, and so forth. Adding one point of Size increases mass by about 2.2 times, and two points of Size is approximately 4.6 times. The formula is MASS=(MASS at SIZE 0)EXP(0.7675SIZE), if you are interested.
Mark
I think people is not reading the spell of ice toughness I posted....
I am turning the body of the magus into hard ice. Level 30 spell. No mean feat there. It is a level 20 spell +2 per size modifiers so it works on giant-sized targets. Quite a few comments on it being unbalancing I feel might be slightly overboard since it is a level 30 spell. A level 30 spell to me MUST be unbalancing. It is a spell thought to go against dragons and the like as the opposition, not meagre human foes.
I fail to see why transforming to supernaturally tough ice should be any harder than that, really....
I used the terram guidelines, not the aquam ones. For aquam it would be to create aquam in an unnatural shape as well (moving ice) so it would be level 4, not level 10. Base 4 +2 sun +2 size = level 20 sopell to change a whole giant into ice. Lower than the current spell, not higher. This is the "densely packed supernatural ice" described by Ultraviolet.
The magus is piling as much as 80 levels of effects on himself to become and ice giant armedi with a chunk of ice. I can think of loads of things that can destroy such a giant by a blink of an eye if they are packing 80 levels of effects into 3 spells. Hell using extremely restrictive guidelines I think you could destroy England with 80 levels of spells and some thought.
For one think this cannot be used in inhabitated environments without the quaesitores yelling at you no end if used against human foes. It is not subtle at all (can be seen for miles around when you use it) so its use is limited to supernatural combat in far away places most of the time. Big places to boot since he cannot transform to an ice giant in secluded spaces.
I wouldn't say that this is something about me trying to powergame here, but it is mostly descriptive cool statistics. I find the concept to be cool, and I am playing accordingly. I can think of quite some better ways to hunt down supernatural creatures (plain old PeAn spells can kill most animals easily by multicasting the low level spell) but they are duller, IMO than batteling them on their own terms with a creature of their own size (or slightly smaller) in honourable combat.... After that, he is likely to spend 1 season doing nothing more than recover from his injuries. I think he deserves some clout, don't you think? 
Still, a meagre +10 toughness might be better after how the +15 soak was received. +15 soak being on the level of a total laughable giant to start with. If going for a mere +10 toughness I will flatly refuse to accept any kind of special vulnearability to fire, though.
Xavi
To get back on the track of the origonal thread:
I don't think this Ice Giant is unbalanced, After all, it's a lot of levels of effect. Soak +10 isn't that much (of course, his wound level intervals are a lot higher, so...).
But an ice giant should have some extra vulnarability towards fire and flame! That said, the Soak to begin with should not short-cgange him, since CrIg spells seem to make up the bulk of combat spells.
I see this as a concept, rather than optimizing. You could get a lot more bang for the buck - and efficient bangs also - with the same levels and time/resources spent. This is very indiscreet, can't be done where no collateral damage can be accepted, and prolonged use of the giant form leads to Warping.
Go for it.
My thoughts exactly. excdept for the flame thingy. For a meagre +10 soak trequiring an extra level 30 spell I will make it as hard as titanium. No extra fire vulnerability. +15, but only +5 if hit by flame spells sounds OK to me, but packed ice providing only +1 soak over a suit of chain mail when you are a 12-16 metres high giant? That sounds preosterous for a level 30 spell to me.
Take in mind that byu the time that the effect is triggered, the magus is a block of ice! It is made if ice (or extremely cold stuff anyway). The previous MuCoAq spell just did that: turn him into an ice giant.
As a side comment I started to see the magus BECOMING an ice giant if he overdid it. Maybe in a hundred years time some flambeau will be hunting Glacius, the ice giant of the pyrinees....
And as a side comment, can you frosty breath of the spoken lie a frost character?
Xavi
I know, my thought was that transforming into an ice giant would be enough by itself to add a little soak as well.
Hmm, wouldnt you need Co as prerequisite, as that is still your "true nature"?
Not even close. A bullet that is stopped by 5cm of steel can still go through a meter of pure ice. The low density penalises the ice very badly when it comes to protection.
You CAN get ice extra hard without making it "supernaturally" so. Its basically a matter of getting ice like in the middle of glacials, where the ice is under such high pressure that it actually behaves like liquid(added bonus, a person made from such ice could move relatively well). However, applying this to something not under such pressure, i would probably add several magnitudes for the complexity in keeping all that ice under such extremely high pressure.
+15 to soak is a major bonus... And it was you yourself that posted:
The "problem" comes from the +5 soak being a base 25 effect.
But i also said you should tack on +1 to soak per size level.
Why? There are tales of giants in myth from most places, as long as you dont do anything stupid, noone should connect it with the order... People will think "-uh oh that darned giant again"; not -"oh get lost you hideous and despicable wizard!".
Direwolf's post seems sensible. I support the Psycholdelica idea, BTW. Maybe we should move the covernant to Ibiza instead and start the macrodisco movement there.
So the original giant would have
LEVEL 30 MuCo(Aq) +6 size giant made of ice.
+12 strength
-6 quickness
+6 soak (soak instead of stamina to prevent it helping in spellcasting)
Add a second effect to turn the ice of the body into HARD ice using the corpus guidelines? Base 25 D: Sun makes this a level 35 effect for a +11 soak overall (+13 counting the +2 stamina of the magus). To me it still sounds really weak considering that stellatus makes +20 damage (plus attack bonus).... A meagre +5 soak for a level 35 spell is awfully high IMO given that we are talking a 12-15 metres high giant made of ice and frost...
However, I feel that the glaciar comment smells opf modern physics here. Making ice really hard is not an unheard event in MYTHIC europe (I underline the mythic component here). Ice giants are not a novelty I am inventing, after all, but are part of legends. And they do not die/melt when you approach a zippo lighter to their left foot....
Anyway, let's leave this as it is for the sakes of simplicity. Overall, 65 levels to make a frost giant with a fairly low toughness. I will have to invest in a really powerful attack here to compensate. That ice sword is starting to look like it will need some massive penetration totals to finish out the opposition fast.....
Xavi
Very much so indeed... 
Now how ever could you guess THAT?
Certainly true.
Well, you may take some wounds at times(not bad ones, with the kind of wound levels you get though), but you´re still getting something quite powerful here, so while it might not be hyperpowerful compared to "real" giants, you´re likely to stomp(literally) over almost any opposition without MR of some kind.
Overall i think it looks fairly ok by now.
Hehehe, when you say you´re going to "walk all over" an enemy, that wont be boasting...