@Arthur For clarity, I'm still wondering about this reply I made above:
Can we later on develop spells using non-core guidelines, noting that there are even core spells that use non-core guidelines? For instance, could we ourselves eventually make The Sling of Vilano?
Yes, guidelines from other sourcebooks will be available during play, but on a case by case basis. I have noticed that some of the guidelines in the later sourcebooks sometime represented an uptick in power, or were in directions that I didn't agree with. Something like Sling of Vilano isn't a problem. Others are simply extensions of existing guidelines, which are perfectly acceptable to me.
But others are not so simple. So I reserve the right to deny some guidelines or modify them.
That's totally reasonable. One of the upticks that surprised me was creating elementals v. the core creating magical animals. I'd like to ask now about two potential guidelines in the future then.
The reason I'm looking at them is that they're both lesser versions of the DEO guideline. For demons, I would stick with DEO. But for non-demons, it seems like in a setting where vis is rarer, there would be more interest in slaying magical beasts without reducing their Might. As they're lesser versions of a core guideline, I don't think they are part of that uptick in power.
These are good examples of guidelines that I find questionables. They presuppose an in-depth understanding of how Magic Resistance and Might Pool work, across a whole Realm.
They seem to have been create precisely to game the system and preserve the vis while stripping away the power of creatures, when those are linked at a fundamental level.
They are also far too broad when compared to previous PeVi guidelines. Guidelines for dispelling effects have to be tailored to a single Art from a specific tradition, and require pre existing of said tradition. The two guidelines above apply to every single creatures of a Realm, be they dragons, ghosts, werecreatures, nature spirits, etc.
The guideline for DEO is just as broad, of course, but it represents a brute-force approach. Such an approach does not require in-depth knowledge or tailoring the effect.
Now, if you eventually have to face a dragon and want to develop something specific, then we can talk about it. 
Fair enough. It was important for me to ask while considering possible Magical Foci. Thanks.
While asking about spells stuff, I should also ask about potential future Mastery choices.
First, does Adaptive Casting exist as such? In some other way? A long time ago I presented some major issues surrounding Adaptive Casting: General Spells Guide (post 2).
Second, in the future might it be possible to pick up any of Ceremonial Casting, Precise Casting, Rebuttal, or Unraveling.
Ah, yes, the Spell Mastery can of worms. 
Adaptative Casting: There is only a single mastery ability for all levels of a General spell. The first mastery option of a general spell must be Adaptative Casting, even if you only know a single version of the spell. Everyone has access to this mastery. (I get final say on what is or isn't a General spell.)
Other non-core masteries: Yes, some of them may be accessible, but they will require story events. Consider them the equivalent of Minor virtues being taught through Mystery initiations.
I will add that to the House Rules.
OK. Cool. Good to know, especially since I was considering starting with Aegis of the Hearth.
OK. That sounds cool.
I should ask about Wizard's Icy Grip, then, since the first level of Mastery may have to be Adaptive Casting.
Guys, I'm planning on taking Aegis of the Hearth (ReVi 20). I could start with it as high as level 35. But this won't cost as much vis, and I'll get about 20 penetration when casting it. That assumes Life Boost does not apply. Taking a higher starting level will cost some penetration as well as eat into my other starting spells
@Arthur I'm now looking at only two customizations of core book spells:
Unraveling the Threads of Vim - Unraveling the Fabric of Vim at R: Touch
Sustaining the Demanding Spell - Maintaining the Demanding Spell at D: Moon
The rest are straight from the core book: Wizard's Icy Grip, Demon's Eternal Oblivion, Aegis of the Hearth, and Suppressing the Wizard's Handiwork.
LVL 20 is already nice, Thanks for the sacrifice on starting spell already. We'll eventually take a higher lvl when we'll learn a Wizard communion at special duration working on ritual to help you cast It.
Yes, therein was one of the debates. But it shouldn't be hard to find a lab text for a higher-level version, so it won't take long to acquire that. Mostly we all just need to acquire Day of Communion to get that nice penetration boost.
Accepted
Oh, and I'll probably just go with "cold" for a Minor Magical Focus. It's fairly limited, but it should be fun.
I'm not sure if we're building companions for this, but I'm looking to have a warrior with Faerie Upbringing and Faerie Friend (a sprite that follows him around as a 'squire'). Possibly with Strong Faerie Blood and either Enchanting Music or Entrancement. I'll share more details as I build the sheet.
For now I am in no hurry to build companions. Let's wait until the covenant is more clearly defined and you know what the needs are.
But be aware that characters with significant faerie links will not be allowed, as that would interfere with the mystery of the disappearance of House Merinita.
That's actually very good to know, thank you.
What Layout do you want for the character's description ?
First post, just the game stats and notes (if any). Second post, appearance, background and history. Further posts, things like familiar, talisman, magic items, lab, etc.
Not particularly worried about a specific format. Don't waste time making tables or anything like that. If something is missing or an issue pops up, I'll let you know and you can edit it. If it's really minor (like a typo) I may edit it myself.
Here's where I am right now so the stats can be examined by SG. I've got most the background written up; a bit cliche but also with some open ends that are unknown, some of which could connect to the main story line. Most importantly, Driven is "determined to protect the Order from enemies within and without" fits the setting well, though I guess Ambitious with heading toward being a hoplite, an archmage, etc. would work, too.
Alis of Bonisagus, filia ?
Characteristics: Int +3, Per +1, Str 0, Sta +2, Pre +1, Com +1, Dex -3, Qik +1
Size: 0
Age: 27 (27)
Decrepitude: 0
Warping Score: 0 (0)
Confidence Score: 1 (3)
Virtues and Flaws: Affinity with Perdo, Affinity with Vim, Cautious Sorceress, Covenant Upbringing, Diabolic Past, Driven (major), The Gift, Hermetic Maga, Life Boost, Life-Linked Spontaneous Magic, Limited Magic Resistance (Corpus), Minor Magical Focus (Cold), Puissant Magic Theory, Puissant Parma Magica, Skilled Parens, Susceptibility to Infernal Power, Unimaginative Learner
Personality Traits: Brave +2, Determined +5, Loyal +3, Methodical +2
Reputations: -
Combat:
| Weapon | Init | Atk | Def | Dam |
|---|---|---|---|---|
| Dodge | n/a | n/a | +2 | n/a |
| Fist | +1 | -2 | +2 | 0 |
| Kick | 0 | -2 | +1 | +2 |
| Gauntlet & Heater Shield | +1 | -1 | +7 | +2 |
Soak: Stamina 2 + Protection ? + Form = ?
Fatigue Levels: OK, 0, -1, -3, -5, Unconscious
Wound Penalties: -1 (1–5), -3 (6–10), -5 (11–15), Incapacitated (16–20)
Abilities: Area Lore: Stonehenge Tribunal 1 (Hermetic Sites), Artes Liberales 1 (Ceremonial Casting), Athletics 1 (Dancing), Awareness 1 (Alertness), Brawl 1 (Gauntlets), Charm 1 (Seduction), Concentration 2 (Spells), Etiquette 1 (Hermetic), Finesse 1 (Speed), Folk Ken 1 (Men), Guile 1 (Slippery Truths), Infernal Lore 1 (Demons), Intrigue 1 (Hermetic), Language: Brythonic 5 (Welsh), Language: Latin 5 (Hermetic), Magic Theory 3+2 (Spells), Organization Lore: Order of Hermes 1 (House Bonisagus), Parma Magica 1+2 (Vim), Penetration 1 (Perdo), Philosophiae 1 (Ceremonial Casting), Profession: Scribe 1 (Illumination), Single Weapon 1 (Heater Shield), Stealth 1 (Indoors), Swim 1 (Underwater)
Arts: Perdo 11, Rego 9, Ignem 8, Vim 14
Casting Sigil:
Twilight Scars: -
Equipment: Heater shield, ?
Encumbrance: ?
SPELLS KNOWN:
Wizard’s Icy Grip (PeIg 30 / +31), Mastery 2: Adaptive Casting, Multiple Casting
Demon’s Eternal Oblivion (PeVi 20 / +27)
Unraveling the Threads of Vim (PeVi 20 / +29), Mastery 2: Adaptive Casting, Multiple Casting
Aegis of the Hearth (ReVi 20 / +28), Mastery 1: Adaptive Casting
Suppressing the Wizard’s Handiwork (ReVi 25 / +25)
Sustaining the Demanding Spell (ReVi 35 / +25)
APPEARANCE:
HISTORY: