I've made one build which used Modular Abilities without ShapeShifting, for when full spellcasting would be overkill but the character would still want some flexibility. It is a good question though, and I'm not sure if doing so is RAW-legal.

I also don't know if it's actually allowed under RAW, but I personally would allow it. IMO, your appearance would change just enough to accommodate whatever abilities you were using. Maybe more, if you added Human Form to it, but still retaining the same general shape.

If a player asked me this same question (I.E. "I want to heal all damage instantly and as it happens")looking to buy powers my immediate response (and that I would guess of many people) would be "You're looking for the Physical Immunity power. Take that and simply "Reskin" it as a ridiculously fast healing." Would I be wrong?

I believe that's how it works for ol' Nick in the books. I seem to remember him actually being affected by attacks, with it just not sticking.

How odd. Infinity is considerably larger than 45.

Woah, careful there. I could make a decent argument that that is not necessarily the case...  

No one ever said anything about a weapon: "Infinity" anyway. A plot device weapon that kills you no matter what doesn't even need a weapon rating-- the result is just what you say it is, no more, no less. That is to say: unavoidable death.

I agree with sinker, if only because in a Submerged game, it's more than possible to use eight refresh worth of hunger-related powers in a single scene, and it's bad enough trying to defend against a static eight shift attack without having to worry about it possibly being as much as 12 shifts to beat (impossible without at least +3 in bonuses).

I'm kind of intrigued by all this talk of mechanic-less games. It looks as though they work very well, given admiralducksauce's site and the testimonies here.

But I'm a pretty crunch-headed guy. I actually enjoy online white-room combat in FATE. And I've never played a game without solid rules.

So, I can't really comment on such games.

Can someone who knows them a bit better say if their requirements are any different from the requirements of a mechanically-based game?

Actually, DFRPG is the first roleplaying I've done with rules. There was still character creation, character progression, and stats, but any actions preformed succeeded or failed based almost entirely on OOC agreement (sometimes explicit, but mostly implicit) between the two sides, whether that was between individual players or between a player and the GM.

Again I would have to disagree on this there a several examples of Jedi and Sith fighting 1000s of opponents (mostly in the Old Republic), there is Darth Nihlus  who can eat all the life in an entire planet and Exar Kun who used force push to cause a supernova.

And I disagree with you. Those are plot device level characters, not playable characters. Or otherwise characters temporarily exceeding their refresh during plot device level events.

What if the character were to wear a hat with a wide, circular brim (such as a traditional wizard's hat), and then empower the hat brim as a magic circle? Would that work as a portable magical barrier that would help rein in the curse?

IMO, yes, if the brim was wide enough. However, portable doesn't mean mobile. You power up the circle, and it will only keep working while you remain stationary. Of course, that might mean that even a slight head movement could break the circle.

So, in the OW entries for Slate, Fix, and the other Summer Knight, the catch for their Toughness power is "Trappings of Winter(for the Summer Knights)/Summer(for the Winter Knight)". My opinion, based on in-book anecdotes and logic, is that this is backwards. Summer Knights should have the catch "Trappings of Summer" and Winter Knights should have "Trappings of Winter". Now, I now this might initially sound crazy at first, so hang on to your britches as I explain myself.

Exhibit A: In Small Favor, Fix confronts Harry and Thomas while they are parked. There is snow outside, and it can be assumed that is rather cold weather. Fix is wearing unseasonably light clothing, and is noted to not be noticeably concerned about this. (If I remember the scene correctly.)

Exhibit B: In Proven Guilty, Lily provides protection for Harry's group from the environment of Mab's stronghold(Arctis Tor?), i.e. the extreme cold.

Exhibit C: In Changes,
Now, what does this show us? That the Summer Knight has no trouble enduring the winter cold, that the Winter Knight is not protected from the cold, and that Summer magic can protect other people from the cold.

This makes sense. You cannot easily fight fire with fire, nor cold with cold. While it should be a simple matter for Fix to use his Summer Magic to keep himself warm, how can he use magic related to fire, heat, and growth to easily keep himself cool? If the Winter Knight went up against the Summer Knight and attacked him with Winter's Magic, the Summer Knight should be able to counter the cold, ice, and decay with his own heat, fire, and growth.

On the other hand, knowing that the Knights' power is granted by another higher power(the Queens), what possible reason would they have to give the Knights resistance to their own power(assuming they even could)? There is no reason. On the other hand, providing protection from the opposing court's themes makes a lot of sense and would serve to make the Knights more effective.

In conclusion, the Knights of the Faerie Courts should have the trappings of their own Court for catches, as they are explicitly and implicitly not resistant to them.