I have to disagree with that. A Demesne is a location created by an entity/spirit as a home turf, so to speak, where they have a great deal of control. They can still get beaten there (as we see with Agatha Hagglethorn and Dresden in his own dream), but they have a lot of advantages.

A Reality Marble (at least in the cases of Ionioi Hetairoi and Unlimited Blade Works) is essentially a location created by the entity where they hold a great deal of power, an advantage, and unlock their true potential. We do have some exceptions (Emiya Kiritsugu has a Reality Marble inside of him to alter his body by way of heartbeat and general speed, but that can be Biomancy and Time-like magic)

The similarities are:

Home Turf (entity has a great deal of power there)
It is difficult to escape (destroy it, destroy the entity, or escape through another supernatural means)
It takes the form of whatever the entity wants when it is first created (Agatha has old Chicago, for example, while Emiya has the vast desert with swords).


The biggest differences I see are:

Victims (and allies) are dragged within the Reality Marble, often against their own will, while a Demesne normally has to be entered.
The entity usually has a sole purpose for the Marble, specifically to unlock a special power (Gate of Babylon and Unlimited Blade Works act as a super armory, Ionioi Hetairoi has the army, etc)


With that in mind, I still think they are mechanically close, thus why I commented on it being -2: -1 for the Demesne-like location, and another -1 to make an "attack" (or simply be the effect) to bring others in. From there, I think designing a collection of powers, or a single power, to be utilized within the marble would be fitting, but at a discounted price (very much like Human Form, as it can only be utilized within the Marble).

In the case with Emiya's Unlimited Blade Works, I think it would be the -2 for the Reality Marble (using the above logic), followed by either a collection of points in Refinement (to denote the increase in his magical power or just the number of weapons; Enchanted Items, perhaps?), some increased physical traits, or even a custom, but fitting, power set he would acquire, then grant a discount due to the limitation of only being active within the marble.

Again, my two cents.

The whole Servant thing doesn't translate well from what I've seen. Yes, the Grail tends to do the heavy lifting and grants the command spells (thus why I see it as a bit of Sponsored Magic), but the idea of summoning an entity with the equivalent of a powerful Item of Power (Gae Bolg, Excalibur, Enuma Elish), a extraordinary ability (Reality Marbles), or even just a collection of typical powers (Superhuman and above levels of physical powers, flight, water walking, etc) is just tough to gauge in this game from what I saw.

Just a random thought (and I'm late to the game here), but wouldn't the baseline of Reality Marble be at a -2 instead of a -1? I figured the -1 for Demesne, with another -1 for an "attack" for force everyone into it. I only ask this since we've seen a few Reality Marbles in the series (I can name two, three if you count the Gate of Babylon), and they all seem to work the same way: bring someone into a world of your design (i.e. Demesne) and have the Home Turf advantage.

As for the powers of the Marble, I'm personally at a tossup between buying them as set powers like you have posted, have a collection of Scene Aspects (theoretically an unlimited number since the Demesne allows you to create Aspects), or even some combination thereof. I'm not too keen on some of the costs, or even a better balancing act. Perhaps we should try to scale some of the Reality Marbles of a few of the characters we have seen and determine it as we go?

It makes enough sense, as that is what the theme of Sponsored Magic is (with or without the Sponsor Agenda depending on the realm, of course). A friend of mine was considering using Fate in lieu of D&D after considering options like this.

Which Power List are you referring to? I know there are quite a few out there, and the search function and I haven't really been on the best of terms the past few times.

The list for Sponsored Magic is fun to sift through, just to see the sponsors people have come up with. Interesting, but not ideal for what I'm looking at.

I should also note that I haven't been a fan of Vancian Magic since I started playing other games. I find it too limiting, but that's just my opinion.
So how did all of that go? Did you just use those entities as Sponsors, or did you use Sponsored Magic mechanics to emulate the magic those characters used?

I have a few of my notes with me; will post them if I can tonight.

Here is the changes I would make to Unlimited Blade Works which would include the powers sponsor (Alya) and agenda from the visual novel. 

Reality Marble (Unlimited Blade Works) [-4]
Description: With the help of a powerful force you can project your soul upon the world.
Sponsor: Alya /Gaia/ the World Spirit   
Agenda: This power is sponsored by the World Spirit in exchange for an Eternity as a spiritual guard dog after death. It's agenda is the protection of the world as a whole no matter the cost on an individual level.

On a related note:

UNLIMITED BLADE WORKS [-4]
Description: You can call up weapons from a magical realm inside your soul.
Sponsor: This magic is self-sponsored.
Agenda: As self-sponsored magic, this power lacks an agenda. Compels from its debt generally involve brutal headaches or one's magic going haywire.
Evocation: Unlimited Blade Works Evocations take the the form of spectral swords that appear from nowhere.
Thaumaturgy: Unlimited Blade Works rituals can be used to conjure weapons, including Item of Power weapons. The complexity required to create an Item of Power is determined by the GM.
Evothaum: Unlimited Blade Works allows its user to conjure weapons with Evocation's speed and methods.
Extra Benefits: All Unlimited Blade Works spells get two free shifts of duration. Spells with no duration, like Evocation attacks, leave behind conjured weapons that last for two exchanges. (The number of weapons left behind is up to the caster.)

The Mystic Eyes ignore Toughness as well as armour. That's why they cost 4.