infernal ghosts are the spirits of deceased evil persons affiliated with the infernal rather than magical realm. As such I believe a necromancy focus should apply with them.
Drowned men are definitely transformed into magical beings, but it states that it is unclear whether they did in fact die or not- in a world where a necromancy magical focus should be able to answer that question definitively with ease it seems to me that the answer would by necessity have to be "sometimes" in order to maintain ambiguity.
I guess I have another Necromancer related question.
Is there any rules about how a Hermetic can give someone the Ghostly Warder virtue, or remove it from someone?
Hermetic magic has no way to grant or remove virtues, though some other traditions (Gruagachan, Learned Magicians etc.) can. But the Ghostly Warder virtue is pretty much just you having a ghost that has a strong connection to your person, so even those traditions can't grant it RAW (because they can't grant virtues that " provide the character with benefits from a third party" i.e. the ghost.)
Granting the virtue in this case sort of requires that the ghost already exists (in which case you don't need magic to have the virtue) or to generate a ghost ex nihilo, which hermetic magic can't do.
That said there are two options available to a magus that I personally would allow under the right circumstances:
A mystery initiation. This could fit in well with necromancy if the ordeal is framed as a complex necromantic ritual. It still requires there to exist a suitable ghost though, maybe the ritual requires the death of someone close to the character willing to become a ghostly warder?
A character entering the magic realm and accumulating enough vis to gain the virtue. But only if the journey into the magic realm fits this purpose - for example journeying to "the underworld" (an insula aligned with Mentem) to find the spirit of a loved one, or entering a tempus which seems to show a part of your ancestor's life, or something else suitable.
Perhaps I should have used a more specific example. Something along the lines of:
Companion A is mourning their recently slain beloved relative/protector on the site of their death. Necromancer comes along, realises there is a ghost haunting the site of the death. Necormancer transfers locus of haunting to Companion A - thus Companion A gets a Ghostly Warder.
Not certain where I saw this half-remembered plot. May have been an earlier edition of Ars Magic. Or maybe another game system.
I think if the ghost exists and is suitable for becoming a ghostly warder then no magic is required, and the character would just get the virtue as a story element. I don't recall anywhere that ghosts in 5e are necessarily bound to a place (unless that place is their link to the mortal world) and if the character who will get the virtue is their tie to the mortal world (necessary, imo, for the virtue in question) then they would be haunting that character from the get go.
If the spirit isn't really a ghostly warder, and a magus wants to sort of shoehorn a slightly unsuitable ghost into the role of protector then I suppose binding the ghost into a magical item which they give to the character would be the way to go - Hermetic Projects has a lot of good material on doing that (with spells and example items) in the Living Corpse chapter. It's not exactly the same in a theoretical sense as a true ghostly warder, but it would be equivalent to the virtue in practice.
It might be possible to use some sort of instantaneous ritual or item with a permanent effect to give the ghost a personality trait of "protective of wardee +3" or whatever other rules way you prefer to represent a ghostly warder's trait of being a warder.
While not easily (if even) possible with Hermetic Magic to give someone the Ghostly Warder virtue,it is not all that difficult to gain in game. One of the ways to maintain Might is through this very role, as shown in RoP:M. If someone gains the attention of any of the non-physical beings of Might, they can decide to use them as a focus for maintaining their Might.
Yes being a descendant or loved one of them makes it more likely that they choose you. However you might catch their attention for any number of reasons, following you around and using their powers to make life easier (or worse) for you.
While this is generally true I do think it is also somewhat less than the entire story.
There are plenty of virtues that have effects that can be duplicated by hermetic magic. The obvious examples include things like improved characteristics and Great characteristic which can indeed be granted (or removed) by either Creo magic or Perdo magic.
Similarly a virtue like inspirational has a benefit that is IMO reasonably similar to what you can achieve with Aura of Ennobled presence. Almost all virtues that a grant a bonus to physical rolls in certain situations such as e.g. Keen vision and perfect balance can probably be duplicated with MuCo spells.
Even a supernatural virtue like skinchanger could be duplicated by creating an enchanted skin that changes its wearer into an animal.
Effectively removing virtues is usually even easier with Perdo magic.
In short I think it is better to say that hermetic magic in general has no way to grant or remove virtues. As a consequence whenever a hermetic magus wants to grant or remove a virtue they must argue that in this specific situation it is possible with a reference to specific spell guidelines that demonstrate that it is possible.
while someone like a learned magician, Grugachan or vitkir in general can grant virtues or remove them. As such it must be argued that individual virtues are exceptions to the rule with reference to the guidelines for what limits are imposed on the specific tradition.
There are some definite differences between inspirational and aura of ennobled presence- specifically in creating artwork. The points on characteristics however is certainly correct, the skinchanger enchanted item would cause warping if used for a long period of time unlike the virtue, and might need to be custom designed for the individual to avoid warping on activation.
Skinchanger, unlike Shapechanger, is actually an ongoing magical effect which can cause warping:
There are still other differences, though - in particular, you can remake your skinchanger item if you lose it, and you get +3 to soak whilst transformed.
Virtues and flaws are a game mechanic used primarily to grant starting PC's some semblance of game balance. Hermetic magic is fully capable of replicating a number of those effects, including piles of cash, improved attributes, allies, magical items, and so on.
But because CrMe and CrCo (Add +x to attribute) enhancers are available, I'd argue that the lesser versions (add +2 or +3 to specific type of attribute role) are also available. That is: if you can improve someone's Dexterity by +3, you can probably grant them a permanent +2 dexterity bonus (inherent Puissant, basically) to cover Climbing and other forms of acrobatics, or something.
Other alternates would be MuCo effects, as above - although those would be continuous effects, and likely have obvious physical side-effects. (Eyes of the Cat literally give you cat-eyes, for example).
However, I'd agree that State of the Art (SotA) 1220 Hermetic Magic doesn't specifically have any way of easily and directly granting inherent, permanent supernatural power - which is usually described as a virtue on a character sheet. The closest there currently is are the Mystery Cult rules, and to a lesser extent the Apprentice Education rules.
EDIT - when virtues and flaws can be detected in-universe, I'd argue that it's usually an acknowledged limitation to the difficulty of mapping game mechanics to in-universe activities, rather than anything specific to virtues/flaws themselves. So while an advanced Mystery Cult script writer can "sense" that they're adding a major virtue, and that it's just as difficult to add as any other major virtue, that's an abstraction we gloss over for the purpose of the game, not a deep metaphysical truth discovered by the character.
The problem is making sure your murder victim actually generates a ghost, of the right Realm. The Living Corpse section of Hermetic Projects (pg 107 - 108) goes into this a bit, but basically Hermetic Magic can't control even whether someone has a ghost, let alone what type it is.
I suppose you could just keep murdering people until you get "lucky". But the whole plan feels like it's more likely to generate (or attract) infernal spirits than anything else.
depends on who you are murdering. If you go through a monastery in an afternoon you aren't likely to get a lot of infernal spirits, though admittedly you won't get much in the way of useful spirits either...
Incantation of Summoning the Dead implies you can summon anyone, if you have their corpse and they haven't been properly buried or gone straight to heaven. Being able to control the ghost is just an extra magnitude.
So Mr. Monk is a devout believer, has dedicated his life to his faith- he dies and lets assume a canonical purgatory, he hasn't been buried yet, and he can be summoned as a magical ghost? I mean I could see a faerie "copy", but if you can sumon a magic ghost of someone who is clearly associated with the divine then there are implications of levels of cosmology in that which could have elder bonisagus writing papers and doing research for centuries.
Unless you have some actual Divine power, you're not clearly associated with the Divine. So the realm of your ghost defaults to that of the "natural" world: Magic. If you want to summon a divine ghost, you need highly specific target selection for your murders.