OK, here's an assortment of questions/rules situations I have come up with after using the rules for a few days or so. They mostly concern extreme, impressive or otherwise cool stuff;
One-hit-kills
A good sniper aiming at a target from half a mile away is an interesting situation. We have a weapon 3 attack at skill +3, in my sights +2, a sniper aspect +2 (snipers rarely get to shoot more than 1/day so they should spend their fate pts), and the target's active defenses are at mediocre (+0). Assuming equally lucky rolls, that is 10 shifts of damage. Assuming best roll for sniper and worst roll for defender (a 1 in 65536 chance), that's 18 shifts of damage. The problem here is that if the target is a PC or equivalent (say, Harry Dresden), there is no way one can kill them with a sniper rifle; without extreme consequences they'd need 17 stress to KO, with the extreme consequence they'd need 26 stress. Even if the attacker is Kincaid (superb skill) and uses three aspects, the PC only dies in the worst possible roll.
How would you adjudicate a sniper vs PCs? A sniper PC vs an important antagonist?
Armor vs light weapons
You have this very tough demon guy(armor 2-3). He won't be undamaged by a grenade or a high-powered rifle but he would laugh off light weapons. Then comes a little girl and smacks him bare-handed from behind. He is surprised so mediocre defense and the girl with fists 2 rolls well for a great result. Suddenly the bullet-proof demon takes stress from being hit. By a girl.
In short, light weapons-especially human fists, a tiny knife or a BB gun-doing damage vs armored targets does not make much sense. How would you fix that? Does it need fixing?
Death Curse strength
Flavor-wise, a weak spellslinger would do a small curse. A more powerful spellslinger would do a significantly stronger curse. Rules-wise though, your curse is a one-action ritual with complexity equal to all your consequences (tagged or inflicted) plus your Lore. That's 40 shifts for the weakest practitioner, 50 shifts for someone like the Merlin. 40 shifts obliterate just about any mortal outright, and most non-mortals. 50 shifts do the same on 5 zones at once. Shouldn't there be a bigger difference between the two, especially at the low end? As is, it is almost impossible to avoid even a minor death curse. (Unless you're Cowl)
Massive Area Spells
Most effects progress at a +1 means double the strength or even +2 means plus one order of magnitude. I.e. conjured object size, lifting weight, weapons equivalent to a certain weapon rating, strength of enchanted items and so on. Time has a similar scale. So it is doable to blast apart something really tough (see below) or engineer a curse lasting for generations.
Area of Effect on the other hand is pretty linear. 2 shifts for 1 extra zone. This means it is almost impossible to cause damage or effects on a more than building-sized area. Even a strong ritual prepared for a day or two and with some aid (about 40 shifts) could at best blast 15 zones for a strong effect. So how do effects like hexing an entire city, causing a volcano to erupt, killing two hundred enemy minons in one blow, killing non-necromancers within a mile and so on work?
Taking out buildings
That was one of the first things that came to mind. How do you adjudicate intentionally taking down buildings and barriers? One rules-relevant way I thought of was this: Take the building's weight and/or size. Calculate the Might level to lift/move that weight (I believe +1 might means twice as heavy weight, right?). Applying force equal to its own weight on the average building would make it collapse, if slowly. +1 for heavily built buildings and those that can handle massive weights or earthquakes, +2 for unfortified metal or fortified concrete, +4 for unusually resilient buildings like nuclear bunkers, the pyramids, very large dams and Arctis Tor. That's the roll you need to take down the building either with might or with appropriately humongous damage. Buildings do not have a defense (unless warded) but don't take extra shifts of damage for high success rolls either. Shifts for taking out well-known buildings in one blow according to this:
Brick House: 11 shifts
200 m skyscraper: 16 shifts
The Empire State Building: 22 shifts
Hoover Dam: 28 shifts
Do note that buildings won't be considerably damaged by minor effects. If you want to adjudicate repeated blows, give them a stress track equal to half the shifts (round up) and armor equal to what remains. A house won't be damaged much by less than Weapons 5, a skyscraper by less than weapons 8 and the Hoover Dam by less than weapons 14. Damage still happens but not enough to threaten the building's integrity in a reasonable number of blows.
Custom Powers (please critique)
Multispell [-2]
Requirement: refinement 5
Benefit: when targeting multiple enemies with magic, either keep your full success roll and spread shifts for effect strength, or keep effect strength and spread your success roll. You're effectively casting one effect of undiluted strength and attempt to hit all targets by shifting the power to arc through them or divide the power and cast a smaller effect multiple times.
Greater Multispell [-2]
Requirement: Multispell
Benefit: when targeting multiple enemies with magic and spreading the shifts for effect, you may affect some targets differently than others. Make a control roll against the total power of the spell -1 for every target you want to affect differently. If successful, you can channel the energy into other effects as you cast. I.e. you call up 8 shifts of power at control +10 and successfully cast. You divide evenly on 4 targets for a weapon 2 effect but you decide you want to blast two normally, inflict an aspect on the third and use a block against the last. You roll again at control 8 (-2 for 2 additional effects) and succeed. The final effect of your magic is 2 blasts at weapon 2, a minor block at strength 2 and the "off-balance" aspect on the last target.
Effectively, you are using energy for one big spell to cast multiple minor magics.
Extended Reserves [-1]
Requirement: Superb conviction, High Aspect involving magic.
Benefit: You have one additional minor mental or hunger consequence. You can only use up this consequence to fuel the use of powers needing mental stress expenditure within one scene, usually Evocation magic.
Special: You can take this ability up to 4 times. You can only take one such consequence per spell. However, those consequences are tagged or compelled as one; if you have taken three of them to keep casting magic, an enemy compelling would get a +6 against you. Effectively, you are learning to draw deeper on your own reserves, pushing your mind at the cost of greater fatigue.