Something just occured to me, and it is so simple I can't believe I didn't notice it before.
Hermetic magic needs to perceive someone to affect him, at least directly.
So, it seems that, unless you've got other means to perceive your target, a simple invisibility spell is a very good protection against most magics.
Worse still, Wizard's Sidestep, while being way easier to cast, draws attention to your image, not you, and thus, it should be targeted, and so, you should be fine.
Withard's sidestep is easily countered with spells affecting the area. A good old fireball or an a Perdo Terram effect should do the trick, and there is a level ten spell specifically to counter it (restored image).
Invisibility is quite a boon, if you can surprise your enemy, but otherwise you just work a counter-spell (CrAn: the humanoid shape where the mosquitos do not fly, IntAu: the the humanoid hole in the air, MuAu: the Air that is not pink, CrAq: the humanoid water-shape in a downpour, Co-spells only with arcane connections, InIg: see body heat, InIm to see through invisibility, Mu(In)Terram: to make the footprints visible, InVim:
See the spell, the caster, the vis carried or enchanted items, PeVim: undo the spell).
And lets face it: If you want to surprise an enemy, you can do better than invisibility. The things you can do with Arcane connections are scarier than mere invisibility.
I think in a mage vs mage duel, invisibility is a wasted spell (not against munadanes, though). You never know if your opponent has something like second sight or an item and can fry you anyway.
If I had the initiative, I'd try some offensive low-level effect, like sleep, followed by a mundane application of a knife.
Both spells work best in crowded areas (e.g. a fair) because of the collateral damage a fireball does.
By the way, does InMe detect the minds of invisible people?
Indeed, ‘tis true. However, invisibility as-is has its drawbacks – still casting a shadow, for one thing. I’d argue that a shadow is sufficient to “perceive†one’s target. The resourceful magus also has several ways to see through or avoid invisibility. Filling the area with water, sand, mud, or a fine dust, casting Vision of Heat’s Light or Eyes of the Bat, and spells that target a large area all come to mind. Second sight is popular as well.
Sidestep is a tougher problem, though. If you use water or sand and try to detect the “real†location of the invisible person by his displacement of, say, created water, wouldn’t the image also displace the water?
On the other hand, is perceiving someone’s image slightly displaced from his actual location enough to have “perceived†him? Would this vary depending on the spell? For example, would Pilum of Fire strike the image and miss the magus? What about Wound That Weeps or even Touch of the Goose Feather, which don’t really seem like they could “miss�
Well, if you go for offensive power, try PeIg (!) A spell that causes the target to loose a fatigue level is level 10 with voice range. Master ist (Score 4) and go for casting copies, penetration and whatever you like.
This way you can render someone unconscious within a single round. Than you can either take him prisoner or give him the killing blow.
This way he will not wake up when falling to the floor.
Another benefit: This single spell works on humans (magi included as it is a low level spell...), fay, animals, magical creatures, ...
However, if two magi clash and have to roll for initiative, both of them did mistakes beforehand. Preperation is more valuable than anything!
I think that Wizards Sidestep would not prevent direct attack spells working on the magus. The attacker is still able to percieve his target and the spell directly effects the target (once MR is overcome) so it would be no defense. Although I think the spell effect would be seen on the image so it would not reveal the actual location of the mage.
However it would be a good defense agaisnt indirect spells as they are aimed they would hit the displaced image (although of course a big pit may well still get the mage ).
Anything which prevents the attacker percieving the target will give protection against a spell attack so Invisibility is a good choice.
Vetrenius: while the YSMV and all that, my call would be that multiple applications of the spell at the same time will not cause additional fatigue damage - it is far more likely to cause actual physical damage (as the temperature keeps dropping).
Make it a trembling spell: you suffer such a chill thyat the trembling and cold make you lose a fatigue level.
You recover (except for your breath).
You are hit again byu the same sopell. trembling of a fever and chill all over again.
You recover
Rinse and Repeat....
I can see this working easily to make the poor victim drop several fatigue levels at once by a barrage of multicasted spells.
IN fact, now that summer is coming in the northern emisphere, you cvan test it yourself. Stay in the sun, baking yourself dead. Enter a building of those that have air conditining at 300% and a general temperature of minus 10 celsius degrees. Step outside after sneezing a little bit. Step inside. Rinse and repeat. You are likely to become ill, fatigued, unable to concentate and jum,py. To mee that is like droping 3 fatigue levels in a very short period of time. Fatigue levels are not only actual fatigue, but everything that makes you way less able to operate normally. That would be an easy case for it.
I too noticed the power of PeIg as a mage killer. Nothing like sweet, sweet fatigue drain. I have my Andorra character doing exactly this already (Mastered Multicast Wizard’s Icy Touch = love).
I think Andrew is probably right about Sidestep, now that I think about it.
Well, he doesn't perceive the target but its image. Quite a difference there
Following andrew, a PoF would be "aimed" at the image perceived, but woulnd instead strike the "empty" space where the magus is, ignoring entirely the image the caster thought to be its target?
This seems wrong, akin to throwing a spell at a mirror in order to strike an opponent hidden by a wall.
As per area spells, of course These are the indirect means I refered too. Yet another reason for magi to cast fireballs
Not quiet what I meant.
As I understand it the spell is targeted by being able to percive the species from the target , a ReIm spell just moces the specie so they still originate from the mage, in the same way I would allow a directed spell to target someone seen in a mirror.
Except for Aimed spells , in 5th edition a resisted spell directly effects its target the Pilum effect is largely cosmetic .
(In 4th Ed I would have said a Pilum of fire could miss as there was an aiming roll)
So let us consider two spells
Bob's flash of incinerating Fire
Base 10 does +15 fire damage to the target , +2 Voice
-This spell creates a burst of fire around the victim doing +15 damage
and Pilum of Fire
Would you allow Bob's flash of incinerating fire to hit the target while Pilum of Fire could not. Or clenching Grasp of the crushed heart?
There would just be a strange visual effect the pilum impact would be visible on the sidestepped mage , the interesting point is if the Fire trail went to the image or to the real mage. I think the fire trail would seem to reach the image
HoH: Societates Flambeau section does cover a few aspects of the debate. IIRC aimed spells will target the illusion or at least suffer a penalty if its invisibility while area of effect or direct target spells that don't involve aiming will hit the magi.
It seems to me that this should also apply to wizard's sidestep: If the magus thinks the image to be his ennemy, he hasn't located him, not really.
Even when he know it isn't so, all he knows is that the guy is somewhere.
As told above, he can then cast simple magics to locate his opponent, or try the Per+Awareness route in order to ascertain his location.
Assuming the attacking magus didn't have Second sight or discern images of truth and falsehood I'm still not convinced that the magus is immune to magic
All the magus needs do is 'percive him' not the 1st spell may bounce but the your average magus is going to recognise sidestep.
However if the character is on soft ground or being buffeted by snow, then his moved species are not going to stop the snow but he is, even if his parma bounces magic.
Id say you could use the fighting an invisible opponent rules form societas with a few minor modifications here. Remember look for things like shadows etc. It's a common trick as a shadow is the absence of light not a projection of species so isn't moved in much the same way a character who is invisible still casts a shadow.
IMO, yes, things would probably look like this.
If the attacking magus is unaware of his opponent having sidestepped, the first spell (unless area of effect or such) fails.
Then, he'll very probably understand what happened, and find ways to perceive his opponent (or dissipate the sidestep, or...)
Creating some snow is a good idea there.
Using a simple level 05 CrTe spell, one could create 10 cubic paces of mud for diameter duration. Quite enough usually.
I would usually think that magically created media as per pg 85 of the main rules would state that ti must penetrate parma as magically created water doesn't even make a magus wet.
The way I've heard about it being done is abusing the parma. Fill a room with black smoke and use true sight of the air to find a magus shaped 'hole' in the smoke and target that.
Thats exactly why it ISNT pointless, because it will be quite visible if somewhere, you get water going sideways and avoiding a personshaped area, dont you think?
It is a really cool attack spell 
These are the indirect means I refered too. Yet another reason for magi to cast fireballs 
