Given the primary purpose of the Development thread is for characters and it's lengthy already, I suggest Vortigern and I move the discussion of his retinue to this separate thread. It might make it easier for us to keep track of the discussion and others can choose to comment or ignore as they feel.
This first post can then become a resource and when finalised/edited, and can be linked to the House Rules thread.
Cheers,
Lachie
Regarding Ludovico's Summoning:
OK, this is very helpful. It might be worth calculating what your standard Summoning and Commanding Casting Totals are without Penetration Bonus and listing them as follows:
Summoning CT = X + Penetration x Arcane/Sympathetic Connection bonus
Commanding CT = X + Penetration x Arcane/Sympathetic Connection bonus
that way, at a glance Marko (and or I) can rule on the fly as given your focus, you'll likely be using these abilities most commonly.
Of course, but he's not been foolish enough to try this so far, eh?
Yet. 
Yes.
For spirits you have to wing it a bit but a base Magic Might of 10 for a non-magi ghost seems reasonable with Characteristics/Virtues/Abilities/XP equivalent to grogs - this seems to be the "basic ghost" and crops up a couple of times in the published canon. When I asked Eric Dahl about his suggestions for making ghosts, I recall he suggested creating them like Hrools - a basic grog (or companion) template where you purchase extra Might/Powers as Virtues. This seems to have been developed further in RoP: Magic from the way I interpret the published ToC.
In answer to your specific questions, yes they are default incorporeal and invisible (ie. only seen by Second Sight or magic) unless they have an ability to become corporeal (like the Legionaire in HoH:TL or some of the ghosts in Calebais IIRC) and some can cause an apparition that can be seen by mundanes. Both of these are powers which require Might expenditure however and for your minions, you would have to coerce them to do this presumably.
This means that in your tavern scene in Chapter 2, your manservant and bodyguard spirits will be invisible. I'd suggest that your bodyguard has the power to make his sword affect corporeal beings like the Leginonaire from the Tremere section of HoH:TL - I'd even just use a modification of his statblock catered to your Venetian story/character.
Your "mistress" appears to behave as if she's both visible and corporeal from the way you describe her, which means she's a Faerie spirit that has at least these powers - correct me if I'm wrong here. Check out the "On Necromancy..." summary I sent you and the Janni article, which contains rules for how incorporeal spirits might assume corporeality and what limitations there might be. She seems to best fit with a Faerie version of an Aerial Power aligned to Auram, but with the additional Power to assume corporeal form at will. Her Might is probably near the maximum you can summon or control - your story implies that she serves semi-willingly. She might work best if created as a companion by another player even - JeanMichelle seems to have a real flair for this, so perhaps he can help?
The material I sent you should also have the references for HoH:TL, Calebais and TMRE. I'd also suggest checking RoP:Magic as you seem to be one of the few people who have it! (I'm very envious).
Cheers,
Lachie
Am I a consensus of one? 
I don't think you need it to be honest (it's actually quite limited IIRC: restless dead, named animals and other spirits who recognise their name - the latter should be quite restricted) - I think there's more story potential to gather actual Arcane Connections etc for this character.
I think that's correct - I think the author, caribet/Neil Taylor, disucssed this at length in a thread but I'd have to search for it to track it down.
No control and no protection either IIRC, just summons. You need another power/spell etc to cover these aspects.
Err, don't know - would need to check with Erik / book closely but they're separate effects, so if you summon the creature to the circle it should work on it as usual. Note this does not apply for Daimons - you can only summon Aspects of them and they can have multiple aspects which they dissolve at will ie. they are immune to Summoning/Commanding in the usual sense and need Hermetic Theurgy and pacts to ally with (see TMRE). I'm assuming we're talking about other spirits here.
I think this could work although the 2 again are independent effects, with separate sources of power. Might throw this one to the general forum for an opinion - my gut feeling is this gets a bit powerful so I'd tend to say no intially till I'd thought it through a bit more.
You could also use theoretically use the non-Hermetic Accelerated Ability of Warding (from HoH:Societas) to accomplish this - see my sahir draft for ideas on this.
Yes. I've noticed this for a while. 
TMRE style theurgy and RoP:tI Goetia (and for that matter the Sihr Ability from HoH:Societas) don't actually blend very well at all - they both interact with Hermetic Magic, but it's still a bit unclear to me how a Goetic Summoner would benefit from Theurgy Mysteries and vice versa.
Since you're designing a Titanoi character, which is the canonical example of a Goetic tradition which can learn both Hermetic magic and TMRE theurgy, you're coming up against this issue full on.
As I mentioned, I think RoP: Magic will help but it's at least 2 weeks away for me here in Oz... 
Hope that helps,
Lachie
My "Jar of Solomon" update is indeed based on this spell / guideline as the "Wicked jar" spell from RoP:tI, page 122 didn't really fit for what I wanted (the latter mimics Goetic Binding rather than the classic "genie in the bottle" effect).
This seems reasonable to me.
It's essentially a "Bind the (Realm) Spirit..." ReVi spell that binds a particular spirit rather than just a ghost, analagous to "ward against the (Realm) Spirit...". I'd have to check the guidelines but I think this would be Ok without a further increase in magnitude.
This is the Realm specific Vim version of the Realm non-specific elemental Form version of what I describe in the updated "Jar of Solomon" spell. You either can affect all Realms within a narrow Form (Mentem for ghosts, Auram/Aquam/Ignem/Terram for elemental spirits etc) or a single Realm across multiple forms of spirit (incorporeal magical entities - represented by Vim) but not both with Hermetic magic.
There are cases where the former Realm non-specific spell is preferable to your latter idea ie. Jinn who can be aligned to multiple Realms which can be difficult to determine.
Remember that hermetic magic cannot distinguish between Divine/Infernal/Magic easily ie. that ghost or jinn you summon might be an Infernal ghost or jinn and thus immune to your Magic Realm specific spell, even if it pretends otherwise until ready to strike...
Nope. Needs to be a separate spell - it's effectively a circular Ward focussed inwards.
A spirit can use it's powers but IMO needs to be able to target the summoner, so unless the form it's trapped in grants senses it needs an AC.
Worth checking the Saga House Rules on this as Marko has specific ideas on Wards and "Bindings/Prisons" being separate types of spells...
Seems a bit too powerful for just one extra magnitude. IMO you need a separate Hermetic spell to do this - the sahir ability is a non-Hermetic power and thus escapes this limitation.
Spirit Mastery involves several feats:
Imprisonment is really a specialised subset of coercion with a Ring or other duration - the prerequisite being that the spirit is either in front of you (through encounter or via summoning) and you can detect it's incorporeal nature.
IIRC, I make this type of imprisonment a Major Mystery Virtue in my non-Hermetic sahir draft but require that the sahir have Warding as a prerequisite (see section). The sahir then coerces the spirit into the Prison, the inward facing ward effect is activated by the spirit's entry into the object, preventing it from using it's powers without permission (ie a condition on the blanket warding, which renews after the requested activity has been performed).
In summary:
Hope this helps,
Lachie
In the scenes/poses I've written so far for Ludo I've highlighted all of the 'spirit rp' in blue, and my intent with that was that everything in blue was 'invisible' to someone who couldn't perceive the spiritual stuff. i.e. someone without intellego vim or second sight etc.
The reason the Yasmine was interacting with Golda was because Golda is some sort of 'Seer' presumably with second sight. So my default is that they are indeed invisible/inaudable etc.
I can see why leadworker might fit, going back to the original tradition of Gunora. But, if I might suggest, Spellbinding might serve you better 
OR, seeing as how you have a Major Magic Focus in Spirits, how about Minor Potent Magic with a specific type of spirit (say, Ghosts?)?
Which is the Mystery you learned (or were supposed to learn) from Abbadon? (Foul Abbadon!)
I'm honestly, from a gamist POV, not overly fond of spell binding even if it is thematically along the line of magics he would be inclined to use. It doesn't seem to really be of much use to someone who already has a decent Rego Vim score, which means in my mind it really isn't very useful for a pure spirit magic specialist. Mainly because of the option to, without spending vis or pissing off a spirit, extend duration with sustaining effects from Rego Vim.
I can see it as valuable for a different kind of mage that had a different focus, and thus didn't have that option. Then you could be say a fire specialist, able to use your form based magic to affect fire spirits, and then use spirit binding to greatly extend your spells. Very useful.
But for Ludo? I don't see it doing that much for him other than eating a virtue point when he can already take a concentration spell and extend it to moon with regular magic. It is unfortunate, as since it is a spirit form of magic thematically it would be very much in the group of things he would be interested in.
I was thinking perhaps 'Student of Magic Realm', a Titanoi virtue, or perhaps goetic Binding and adjusting his flaws to suit. I'm perfectly willing to drop the leadworker.
I agree. I think Spirit Binding is a bit ho hum for very similar reasons - sure it might be useful if you specialise in an area and do a bit of spirit dabbling but for a focussed summoner it's a bit useless.
This will be a bit controversial but I'd actually suggest taking Sense Holiness or Unholiness even though this means spending 25 XP to raise it to a reasonable level of 3.
From a meta-game perspective, it's probably more useful than Second Sight to a Hermetic Summoner as Hermetic magic can't replicate this power, while it's pretty simple to replicate Second Sight.
This may go part way to explain why Ludo has avoided succumbing to infernal temptation as at least for less powerful creatures, he can tell if they're truly Infernal provided he can penetrate their MR (difficult, but doable - there was a recent thread on this but I can't find it). It's like a counter to his stigma of having a tainted lineage - "hey look Mr Quaesitor I can tell when what I've summoned is a demon so I'm not going to make the same mistake my ancestors did..."
It would have to be aligned to either the Divine or more probably the Infernal realm though. Alternatively, if Marko is feeling mean, Ludo might think it's aligned to the Divine realm when in fact it's a False Power aligned to the Infernal realm...
Perhaps replace Incomprehensible with a Delusion (powers are not Infernal) or similar?
Cheers,
Lachie
Do you guys really think sense (un)holiness would be of use to him?
How would he have come by that power as a divine realm aligned thing? Does that really fit with the idea of sorcerer, if it 'must' be a divine power? And beating something's might with a perception+sense ability roll means, correct me if I am wrong, that it would be largely useless as it would apply to the might of the creatures he would be summoning and dealing with? Thirty just doesn't seem reachable, and that is his 'easy' threshold right now?
How would the study of that ability integrate into his concept of magic? Would it be some new/other manner of goetic/spiritualist training... or would it have to be a thing that wa divinely granted or some such?
Goetic Summoning Total: ( Presence + Summoning ( OR Rego ) + Realm Lore ( OR Vim ) + Aura + Penetration(modifier)+die)
Goetic Commanding Total: ( Communication + Commanding ( OR Rego ) + Realm Lore ( OR Vim ) + Aura + Penetration(modifier)+die )
Ludo's Summoning Total: (1+20+20(2)+Aura+4(Modifier))=61+4(Modifier)+Aura (Chthonic Invocation +20)+die
This means, without an AC, he safely summons 1/2 of this total for a might of about 30 or 35. With a name or other AC this goes up based on penetration, for a fixed x5 AC it bumps him up +10 might, as does using Chthonic magic for a high end 'safe' might of about 50 or 55, depending on the dice.
Ludo's Commanding Total: ( 1+20+20(2)+Aura+4(Modifier))= 61+4(Modifier)+Aura (Chthonic Invocation +20)
Under normal circumstances this would place his commanding at 1/2 this, for the same totals found under summoning. It is worth noting however that using commanding on a spirit already 'in a summoning circle' negates the need to double it's might. This would mean he could theoretically command something of a might up into the 80s, if he could summon it and pass the concentration check to use commanding without losing his circle. That is however a difficulty of approx. 15 on the concentration chart so not something he is likely to attempt at this time. It does raise interesting questions about goetic sorcerers cooperating to summon and command more powerful things together.
Ludo's Hermetic Spirit Control Total/Penetration: (Tech+Form+Stamina+Pen.(Modifier)+aura+die)
(20+20(2)+ 4(modifier)+die) (Chthonic Invocation +20) ( Spell lvl 20) ( Pen. 20+20(2)+4(modifier)+aura+die-20) (Chthonic Invocation +20)= 40+4(modifier)+aura+die (Chthonic Invocation +20)
The compulsion spells have a level of twenty, so his hermetic spirit bindings have a penetration ( without AC ) of roughly 45+die. With a fixed AC this would go up to a penetration of 60. Chthonic magic can add +20, so he would have a high end cap here of a penetration of 80+die.
Realistically, within his summoning limits, he is probably accustomed to handling spirits of might 30 or 40, perhaps the occasional 50, without worrying too much.
His main weakness and corresponding goals are the hermetic spirit magic versions of what he does. Developing those would up his penetration ability with AC range summoning considerably... yet would also necessitate the developing of an array of warding spells to use in accompaniment. He is probably several years of solid work away from having a good repertoire of such spells, but they would up his spiritual power level considerably.
Your spirit powers are interesting and formidible. It just might be enough to save the day one day 
In other words, with what I am planning, the magi will find you quite useful 
It's just a wild idea... 
You're right about the difficulty with Penetration but IIRC, you can use Sympathetic Connection modifiers and Aura bonuses to boost the Total for Supernatural Abilities so it's not quite as bad as all that (Divine aligned powers have no magical penalties in other aligned auras, so if you have a AC/sympathetic connection bonus to whatever you're summoning you could use it even in an Infernal aura...).
Mind you, if you have an AC you might have some idea of the Realm alignement of the creature you summon, but then again maybe not...
With your impressive Summoning total, you could take the hit to your Casting total from a Divine aura (-15 in a church/cathedral still leaves you plenty of room) to help boost your Sense Holiness power by +5 and add some "insurance".
I take your point that it would be useless for really high Might creatures or even what Ludo can summon "easily" now, but I'm making the point that it would potentially have helped Ludo avoid becoming corrupted when he was starting out by allowing him to avoid inadvertently summoning low-level demons, which are much more common and dangerous in some ways because IMO they are potentially more easily mistaken for creatures of other Realms eg. a Might 10 Infernal ghost could easily be confused with a Might 10 Magic ghost and this is where this power would come in handy...
Admittedly, this is a high-powered Saga so perhaps YMMV...
I haven't crunched the math, so I don't know how practical or feasible it is - it was just an idea that I'd wondered about for a while.
Perhaps that's why he was chosen as a Titanoi - he can stand up and say he can detect demons / is divinely blessed and thus less likely to become corrupted? Having powers from different Realms is not prohibited, it's just unusual (and in this case a bit of a stretch I'll admit - you correctly point out that Sense Holiness is always Divinely aligned).
I don't think it could be integrated into his training, it's more like an in built conflict - the Divinely blessed apprentice who becomes a Goetist has a nice irony/paradox to it in a way...
It's just that Student of Realm is so... bland.
Perhaps Side-Effect (after casting, gain a calm state of mind that aids in concentration rolls) - this would actually fir your character.
Cheers,
Lachie
Hmm. Well the other issue is that right now it is a minor initiation slot that I am looking at, which is even more improbable.
But I could theoretically do a little shuffling and put something else in the initiation slot and make the sense (un)holiness ability a thing he had at origin, which would allow me to shuffle some xp towards it more easily as well.
But I'm going to have to think about that. It is true however that his second sight 'combined' with this sense ability would have made him an ideal recruit for a titanoi apprentice. So it does certainly fit into his concept. It would also raise the question as to whether his second sight should be divinely aligned if I do so.
It makes me want to consider the character ramifications a bit though. that would basically mean 'God has a plan for Ludo. See, he gave him powers.' ... which I have no idea how to fit into his concept. Not that it couldn't be done. Heck it could add a lot of flavor to him, especially with him basically being a pagan irreligious bastard. But the conflict is certainly there, with him being a relatively devout titanoi pagan. It makes me scratch my head and think hard at least.
Given that apart from Theurgy Virtues, Student of (Realm) seems the only Minor Virtue that Titanoi can initiate, this may be the default option here.
I intended that you consider Sense Unholiness as a starting Virtue, sorry I should have made that clearer. As for Divine aligned Second Sight - hmm, interesting but a bit of a stretch perhaps and really limits it's usefulness outside of Divine auras in some ways.
Yes, it's an interesting conflict...
Perhaps you could change Pagan to Depraved (Major) (RoP:tI page 88) - Ludo rejects God and shows disdain but does not actually worship Pagan spirits - he has learnt there is more to the world than God from his Tytalus apprenticeship and become atheist (still quite a dangerous Flaw to have in medieval Europe). This might fit better and adds a tragic element - the Divinely gifted child who has strayed...
The Divine moves in mysterious ways, perhaps?
Cheers,
Lachie
I get the general impression that you seem to estimate the danger of a budding summoner / sorcerer being corrupted by infernal forces to be a 'considerable' or 'large' risk. That has not really been my feeling given the rather ubiquitous nature of spirits in Mythic Europe.
Now... Ludo may be at a somewhat greater risk than usual given his pagan/mercurian leanings... but that is another point.
Do you see it as an inherently fatal risk for young and growing/learning summoners that demons will try and infiltrate the spirits that they summon or what-have-you? How about older summoners? Still prone to being actively subverted? It just isn't something I see as being an 'active' threat, unless the storyguide makes a story out of it or it is related to a flaw. You however seem to be rather concerned with the idea of how Ludo avoids this looming fate? Or is this related specifically to your view/estimation that his personality is more prone to attracting demons / being corrupted?
I'm not trying to be alarmist and I don't have RoP:Magic yet (it's on it's way but I usually receive things about 2 weeks later than most of the Berklist/forums as I live in Oz like Timothy. Sometimes I have the rare pleasure of receiving my copy before the line editor receives his in Japan but I think it's only happened once...)
AFAIK in ArM5 canon there is no sure way of telling whether a scoured spirit is Infernal or Magic or Faerie etc (perhaps a concealed roll against the various Lore skills of the character - not sure, might have to ask Erik D on that one). An Infernal spirit can easily trick most summoners that it is Faerie or Magic in nature as Hermetic magic, Faerie magic or Infernal magic is unable to discern this. Divine aligned powers can (Sense Holiness or perhaps a warning from a Guardian Angel etc).
Let's say you avoid scouring and stick to summoning spirits you have Arcane Connections for, say ghosts who have bones available. You can only summon ghosts that have not had a "proper burial" (Christian, Muslim, Jewish or yes even Pagan). There is usually a reason for the lack of a common burial / easy access to the remains - most of these reasons are linked to some kind of sinful activity on the part of the deceased or death by violence / accident etc. There is no guarantee that the ghost will be a Magical one (or a Faerie one) from just scrutinising the remains - you might get an idea that summoning the spirit of a serial murderer or usurer is likely to result in an Infernal spirit, but what about nameless ghosts etc.
You can't summon airy spirits without some form of arcane connection, which usually requires Hermetic Theurgy etc.
True Names in ArM5 canon are only available for demons and Divine creatures - a summoner can't tell these apart just by reading them even if OOC you know that if you study Divine Lore you won't be learning a demon's True Name from the way the mechanics work. In reality grimoires were scattered through with names of demons, angels and "lesser angels"/airy spirits which all gets a bit vague - see Gustav's "Dictionary of Angels" to get an idea:
amazon.com/Dictionary-Angels ... 600&sr=8-1
(incidentally this is a great book for names etc for spirits/entities - it covers most "real sources" but also draws on literature/myth and occultism so it's not that reliable but it's very good for RPG ideas)
In summary, even if you obtain an Arcane Connection to an entity you think is MAgic/Faerie, there is no guarantee in game (except by Divine aligned powers) this is not actually a link to a demon/Infernal creature.
The risk is there and alluded to in the Ars Goetia chapter IIRC.
Possibly another point, but Pagan does not necessarily mean Infernal. Pagan and associated with cthonic dieties (Hecate for example) places you at much greater risk as it's a bit unclear if she is a Magic entity that has become Infernal, always an infernal entity or whether there are multiple entities referred to as Hecate...
I think being a summoner is the risk, not being Pagan.
Not inherently fatal, but it's difficult to avoid the price...
Summoning is tainted, regardless of Realm and carries with it the risk of attracting demons.
Commanding is out and out an Infernal aligned ability, so it's a strong link to the Infernal and the risk of corruption by demons.
IMO it's young summoners that are at most risk as they have the most to gain from "taking short cuts" and may inadvertently summon spirits aligned to the Infernal Realm that they are not powerful enough or sensible enough to dismiss without compromise.
Old summoners are the ones that have avoided the temptation of a quick/easy/corrupt (ie Infernal) path to power and have carefully avoided bargaining with anything they don't know the true nature of / can't command or coerce directly without resorting to sinful powers / sacrifices etc.
I don't think you need an explanation why Ludo isn't corrupt now - he's proven he's smart enough / skilled enough / sensible enough to avoid dealing with demons.
What I think would be an interesting aspect to develop is why he didn't become corrupted by his Goetic powers, when he was still young and most at risk of temptation and folly.
The Sense Holiness idea was just an idea towards that - it's really only useful for low level entities and to a starting character as by mid career the entities summoned are too powerful to be reliably discerned and a summoner needs an alternative strategy to deal with unwanted INfernal spirits...
This is a good point - I'll concede that without a related Story Flaw, it should play a lesser role and hold any Storyguide/Troupe to that.
My point is that these powers seem to have an inbuilt "risk of damnation" built into them as a counterbalance to their IMO superior power strength compared to other abilities.
He is descended from a lineage that succumbed to corruption.
He is a Tytalus, which although not necessarily pone to sin in itself, makes it difficult to avoid sin, regardless of whether he follows Callichean or Hippian ethics - last time I checked there were no highly devout Tytalan magi depicted in any of the prior editions...
He is a pagan, which makes avoiding damnation difficult as although he is not necessarily damned by not following a monotheistic religion (he just has to follow the precepts of his Pagan faith), there is more chance of misdirection and straying from the path IMO.
It's not a big deal - it's just potentially interesting in terms of stories.
Hope that all helped - really I think he's a great concept for a character as it is and I wouldn't let anything I have to say delay you from finishing him off and jumping right into the Saga!
Which seems to be hotting up...
Cheers,
Lachie
Personally, especially given the differing realm alignment of many Vim spells, I don't think an assumption that Vim can not determine what it is dealing with is reasonable. A decent Intellego Vim effect should be able, at fairly low magnitude, determine something's realm alignment.
Now... that said... if anybody could hide from such magics, it would be a demon, so that certainly wouldn't be a foolproof method of avoiding the clandestine demon posing as another form of spirit for the summoner.
The problem I have with this then is the realm alignment of vim spirit spells. Some people seem enamored with how they envision this playing out with a summoner never knowing whether or not he has the right wards up or is using the right version of control spell or whatever but I see all of that as largely things that should be OOC mechanical concerns of the game rather than IC things, unless of course you simply don't have the right spell at hand. It shouldn't be so very difficult to figure out after either an intellego vim or even just looking at the target if you have decent lore skills. Either that or apply your knowledge until something works,and then you know. ( You hope I suppose. ) It comes across feeling rather gamist to me to have a character be a skilled summoner and then say 'Sorry, not faerie after all. 
CHOMP! ' ... I for one would be a rather annoyed player OOCly.
In ROP:M the functioning of true names and even regular names for spirits is given a little bit more attention. I've been sitting on my hands waiting until you all have the book before trying to discuss it, but you beat me to it. Basically in ROP:M it states a few overlapping / related things. All varieties of spirits, if significant enough, can be daimons. All varieties of spirits have names, and all of their names are indefinate ACs. Only Daimon's names are 'True Names' which require the true name learning mechanics of studying a lore/xp.
Also, depending on what type of airy spirit, there are a variety of other things that could constitute an AC to it. Examples are a young romantic couple engaged in courting would constitute an AC to a spirit of love/romance or someone who is angry would be an AC to an anger spirit. Anything that exemplifies the qualities/aspects that the spirit represents constitutes an AC to it. So... knowing this I think arranging ACs of this manner to spirits they want to summon would become something of a highly refined art to a summoner.
That and I think grimoires of non-daimon names would be compiled and studied with the same intensity of daimon level names. Both. But unlike daimons with regular airy spirits unable to create aspects, you then would have to worry about summoner competition and the like. So perhaps they would have incentive like regular theurgists not to share such grimoires outside of their lineage etc.
Don't overlook the HR'ing placing ablating as the only 'infernal only' goetic skill. For our purposes commanding is 'tainted' like summoning.
Which still I suppose has the possibility of, either one, attracting supernatural attention from any direction with their use. But that is sort of the point of the skills... so I'd view that as unavoidable. At least the drawing attention part. Becoming a know force/quantity among the local spirits is something I see summoners desiring. Becoming a force of personality that they view as simply part of the local makeup and obey etc. So... yes, I can agree that they would tend to attract attention spiritually... I think they would often be attempting to do exactly that.
I'm not certain how much 'corruption' should be a factor with Ludo. It certainly should be some, because I envision him sometimes struggling both to overcome the taint of the tasgillia lineage despite his unabashed honesty as to his magic and the pride he takes in practicing the magic of the founder etc as well as perhaps even being tempted/courted by actual infernal powers. I'm not certain how this can/should play out however, just obviously something I think deserves some heavy thought/drama devoted to it rather than every other spirit he summons being a demon.
My general impression with summoning is that you have to learn to take whatever a spirit says with a grain of salt as it were. They have their own understanding of things, largely without mortal morals, and they just might be a demon telling you a great big whopping lie. So, to me, the potential for corruption is two-fold. First is that you get carried away into the viewpoint and world the spirits and entities you are dealing with and stop thinking of the world as a normal human... and start to be amoral and otherworldly/corrupted by that. You dissassociate, and become monstrous from your changed viewpoint etc. Second is that as you progress on number one, you are less likely to balk and realize what is going on when a demon comes along and whispers temptations of whatever variety in your ear. You move towards darkness not necessarily because you choose darkness but because you have lost the perspective in your world to see it for what it is.
I'm not sure if that is very medieval or not though on second thought. Hmm. I'll have to come back to this with more thought.
And in light of ROP:M, I'm not sure if the whole set of rings thing is still workable, or if there might be a way to salvage the idea or not.
I agree that InVi spells should be able to determine the realm of a being. But of course Demons are able to decieve such spells . Anyway, Infernal corruption is definately a poltential storyhook for any summoning type of character, even more so for a Titanoi of an esoteric lineage (as in, stranger and more unique that most Titanoi). How he avoided it all this time? Luck. How will he avoid it in the futire? Who knows. But I am not running a "demons around every corner" type of game.
As far as what Minor Virtue you should take, I say pick Student of Magic Realm and get it over with. 
I promise you it will be useful and relevant.
I don't have a major problem with this but IIRC this is not the RAW. I don't have time to comment further and it shouldn't hold up Ludo's intro in any case.
I agree. Jump into action!
I'll respond to Vortigern's comments and throw a Poll onto the main list when i get back from a course this weekend.
Cheers,
Lachie
You could at the very least use negative testing to determine realm. "Determine Might of a Magic Creature", that failed, "Determine Might of a Faerie Creature", success, it must be a faerie. Same could be done with might-stripping PeVi spells, but this will probably provoke hostility.