If a Magi is standing inside a Rego Vim ward that protects him from a Creature with Magic Might. That creature can't walk in, or use powers in. Can he cast spells out of it and hit the creature? Or would the ward break when he tries to cast out of it.
Secondly.
I have a cart, with a circle inscribed inside of it. I cast a circle ward.. is that ward movable? Does it stay with the cart as the cart moves?
I don't know of any reason why he couldn't cast out at the creature. I don't think that wards should be fair to the warded against creature.
To my knowledge the rules do not specify that the circles are immobile and there may even be examples in the line of movable circles, but... I hate it with tremendous quantities of spiteful loathing. It makes too many things too easy, it never fails to feel cheesy to me, an exercise of rules rather than of magic. (This is naturally a matter of taste, you can run a game either way.)
Well, there reason is that it breaks the system.
If you can just stand inside a movable ward and cast all day. Battle Wagons are a thing, and it escalates aggression pretty seriously. I despise the idea of a movable ward, but I am trying to find a RAW backing for saying no,if there is one.
It is a much bigger deal than just wards any ring circle spell becomes more or less an enchanted device.
I don't consider moveable ring/circle spells (including wards) to be a problem, provided you do it in a rules-environment where the ring/circle is fragile. Even smearing it slightly will break the spell. Being jostled in a cart while casting a spell, to me, is an indication that you will have additional botch dice and perhaps even need a Dex roll to avoid falling down and breaking the ring/circle. And most spellcasting botches will probably result in the ring/circle being broken as well (most often indirectly).
And if you start stacking the ring/circles on top of that... well in any saga that I storyguide, then you are asking for trouble. 
IMHO, ring/circle spells have their use and are a colorful way of performing magic, but they shouldn't be abused. They are designed to be defensive and mostly passive in nature. Trying to turn them into offensive weapons, or into an active defense, is something I consider distasteful.
Erik Tyrrell covered this pretty well. Wards are neither symmetric nor fair.
Destroying an entity from within a Ward is both popular and adviced.
There has been some debate over the years on this matter.
I personally tend to favour immobile Rings/Circles, but mostly for aestethics.
It's one of those matters where my advice would be to discuss it with your troupe, reach an agreement, write down that agreement, and play with it.
As for the specific case of the Ward in the cart, remember that the whole cart is not warded, only the parts within the Circle.
Plausibly a Warded Against Entity (WAE) could damage the cart in such a way as to damage the Circle, thus breaking the Ward.
Movable wards are not restricted in raw and I like them. YSMV. I've never played through an abusive scenario, but the forums have discussed many.
There are many ways to abuse the raw, so discuss with your group (ie. Parma). Blocking a clever use because you don't like it isn't good imo, and there are better ways to mitigate potential abuse than saying no.
I'm not sure how you mitigate a flying level 25 ward that can penetrate without escalating the might of magical creatures. It's like.. yay Flying tank! That seems to escalate the game aggressively. I'm not sure that's exactly a clever use, more than a giant gaping hole in the system.
Hmm. A ReVi 25 Ward penetrating, so that it keeps out Might <= 25 creatures, requires a Casting Total of 50 - give or take adjustments for auras which I will omit here. Look this up in HoH:S p.113 box Wards and Penetration.
This Casting Total is definitely possible. But a single casting of a PeVi 25 Might Stripper with a Casting Total of of 50 takes out a creature of Might <= 25 for good.
Both instances might require that the SG ups the challenge. But this is hardly a hole in the system.
Look up RoP:M p.33ff Season, especially p.34, crossreferencing the Power of a campaign with the Magic Might of creatures supposed to challenge magi.
Cheers
One Shot - agree very much.
Also a flying tank or battle wagon can't be protected by the same wards, so as said above, target the tank not the caster (much like shooting the horse and not the rider).
And I've never seen a player go to great length to build something like this in a game. I've seen far worse rorts of stacking odd virtue combinations to "abuse" the learning systems, or maximise stacked Puissiant virtues; but these are not really issues if the all players are happy with them.
Further if they did expend a large amount of their resources building it, then you've had a lot of time to discuss its use and the fit to the saga.
To be honest, I don;t recall what RAW has to saw about breaking the ring, but classic stories are rife with rings being broken by a leaf or hair floating across it, and IF that standard were to apply, then the ring would break itself as soon as it moved over anything besides the smoothest terrain.
The above is clearly a YSMV and is almost certainly not RAW, but something to ponder regardless.
What about that flying castle from 5e? Did it have wards?
Castle of Thomas? I don't recall any of the effects being wards. His trick was a huge lesser device with a normal castle built upon it, and using environmental triggers which detected if the spell wasn't present, and if it was missing it recast the flying spells.
Hey, folks - speaking as the player that has the portable ward,
It's a floating rock slab, originally designed for cargo hauling but also used as a sort of runabout. (ReTe effect, based on the "magical transport" effects from TME: base speed 17 mph; max ~40mph.) The slab itself is 7" thick or so, and around 8x8 feet. (basically, a 3x3x3' cube of rock, flattened out.) In-game, it was established that the magi threw up the ward as a basic circle when a large magical bird attacked, but upon further discussion it was determined that such a craft would probably already have a ritually-inscribed circle around the outside anyway - simply because it would be too useful NOT to have it there. So it's basically a square with a circle inside it.
The campaign uses 'weak' wards - a temporary (chalk/dirt) circle is broken if you pass any physical object through its sphere. A ritually inscribed circle, in contrast, is suppressed if you lay something across the boundary, but can be broken if the circle itself is damaged.
As OneShot implied - the magi in question threw up a ward because he didn't want to 2-shot the creature with his PeVi might stripper. (ReVi casting total of 37 with a lvl 25 Ward - spent a Faith point and rolled a 45 total), PeVi casting total of 22, has a lvl 5, Touch-based 10 Pt. might stripper and a sight-based Intangible Tunnel with 20 pts. of penetration).
The creature in question nearly shanked the shield grog and the teamster who was flying the slab before the ward got put up. That being said, the fight allowed him to get a blood sample from the creature, and he's an Abjuration specialist. That bird is HIS.
The flying platform is a lesser enchanted item, purchased with build points. (lvl 25 effect). It was the first time it has been used. The magi is a warding specialist, and was in the process of setting up an extended security ward around their base camp (He's got the Circle/Warding virtue) when they ran across a roc-like bird. The circular ward in question was the first spell the magi cast in the campaign.
It didn't use boundary wards, at least. According to HP, pg. 123, "Boundary effects are not, by their nature, mobile. This means that, for example, if the castle had a Boundary ward against magical creatures, it would leave the effect behind as it flew. Similarly, an Aegis of the Hearth ritual cast around the edge of the castle would also be left behind as the castle moved."
Similar issues with moving structures are implied in Through the Aegis, whereby the covenant that's onboard a series of ships has a holy relic in place of an aegis.
However, the section specifically mentions Boundary effects (in capital letters), and specifically addresses the Boundary target. It doesn't mention any other target: structure or room or circle. As you can very obviously target moving structures with permanent spells (as many of the boat enchantments in Hermetic projects are built using T:Structure, and have various T:Structure effects that work while sailing), that suggests that wards can be placed on moving objects just fine - just not Boundary wards.
So, basically - even if circular wards were prohibited, you could still create a warded, flying box (T:Room, rather than T:Circle), and the issue would remain. As such, it seems like a lot of work (IMO) to prohibit moving circular wards - it simply causes the issue to move to a different part of the ruleset. For example - in HP, there's a simple spell to ward a part of the boat against fire, so that you don't accidentally set it aflame with your cooking hearth. If you can ward a moving room against flame, you can probably ward it against a magical creature.
I don't expect a Might 10 creature to be a real challenge. It was really more of a This is what would be here, lets stretch the combat muscles to see what shakes out. And it did almost cause a heavy and a moderate wound to the 2 grogs, and missed it's pen roll by 1. against the mage. My real concern is the .. lMight 25 or less, not a challenge, MIght 30 or more, totally saga wipe. And these are starting Maga. When you consider that an Archangel and a Dragon are supposed ot be might 50.. I seems that Ars has a serious balance issue.
And that 'chart' in RoP:M doesn't really help that much. When all starting mages are created the same, how do you determine low, mediaum, high, legendary? And again, a lMight 10 creature is basically a joke against most Starting Magi.
Additionally, Even though Vim is supposed to be the newest, least mature form.. it's one of the most powerful.
Rego VIm lets you quickly make wards that block all supernatural creatures save for the most powerful.
perdo vim lets you easilly strip might creatures of power from the comfort of your little ward. The muto vim effects lets you fairly easily convert touch spells into sight spells. All in all, it feels like Vim is /really/ powerful, combine it with corpus.. and it's hard for other magi to not feel like they picked the wrong arts.
It really feels like the system is fragile, and if the players don't work hard not to break it, it implodes under it's own weight.
Depends. Sure, Rego Vim and Perdo Vim can be great against supernatural creatures. But by RAW wards needs to penetrate, so the magus needs to be able to double the creature's Might with his casting total. Probably using a formulaic spell specific to the creature's realm, because a spontaneous ward (where you can pick the realm on the spot) won't be able to pull off much penetration. That means each spell must be learned three times at least (if you discount Divine opponents), and you need to learn new higher-level versions as your Arts rise.
I would also note that Vim doesn't help at all against physical threats, be they mundane weapons, wild animals (either naturally aggressive or controlled by magic), rock slides, or what not.
Finally, while one Might 10 creature may be an easy fight for many starting magi, what about 10 of them? Sure, if the magus is inside a ward it is fairly easy to eliminate them one at a time, but meanwhile his grogs are probably getting cut to pieces. Or they may run away and harrass your party -- even magi need to sleep sometimes. Just because they have low Might doesn't mean they are stupid... 
Minor point on that one - the character in question is a Holy Magi whose Holy Tradition includes Abjuration: this is actually one thing such a character won't have to deal with, once he learns his Method/Powers. While Abjuration does have the standard "General: Ward against X" guideline (identical to the ReVi version, basically), it also has a "lvl 15: ward against all non-divine entities" effect, with no restriction regarding Might. So once the character has that, he actually only needs to learn 1 lvl 30 ward (Base Effect +1 Touch +2 Circle/Ring), which covers all non-divine creatures, and resists for as much penetration as the PC can pump into the spell.
To be fair, that's relatively deep into a character concept (3 major virtues up through Divine Spellcasting, and most of the guidelines are near-duplicates to ReVi) - and it comes with all the restrictions that Holy Magi have to deal with. But the point about it being a restriction isn't quite as much of a gate as it normally would be in the general case.