You know, my Verditius (likely the most poorly-created least-optimised Verditius around) has Tethered Magic. He uses it quite a bit actually.
I'd love to be able to enchant devices that take advantage of Tethered Magic. I'm not sure that's within the reading of the Virtue, but I'm prepared to give it a go and see how quickly my troupe shoot me down.
I'm going to go on the opposite opinion:
Make it a regular bow. Enchant the bow with a few effects: PeIg to extinguish a torch, ReCo to knock someone unconscious. The range is Sight. It seems to me like the arrow is a largely cosmetic effect, in the same way that the 'mist' in Frosty Breath of the Spoken Liar or a green Ball of Abysmal Flame is a mist.
I was thinking the same, but he wants to use his Bow skill to actually hit targets. It's a character thing....
I'll take a look at Tethered Magic.
I would go with an enchanted device with multiple effects. Not ALL effects, but you can enchant quite a few level 10-20 effects on a bow if you chose the effects with care. A talisman perhaps? The arrows are part of the casting effect, along with some gesture, positioning of the bow or word. With tethered magic you can easily release the effect with the arrows. You might need Touch range with the bow, but then your effects need an aiming roll, since it is the arrow that actually release them at the point of contact.
Sounds like a feasible project to me 
Cheers,
Xavi
Hi, allow me to introduce an official spell from True Lineages, with Tethered Magic:
HUNTER’S LETHAL ARROW
R: Touch, D: Diam, T: Ind, Level 40
This spell causes an animal to suffer a fatal wound, just as if it had been pierced through the heart. Casting this spell while intending to touch the animal is dangerous, as it may take several minutes to die, during which time it may thrash around wildly or strike the caster. For this reason, Milvi usually tether the spell to an arrow or javelin (though any sort of tether may be used), allowing them to cast it in secret from a safe distance. The beast will die after it is struck, and the increased duration ensures the caster has time to fire the arrow after casting the spell.
(Base 30, +1 Touch, +1 Diam; Tethered)
As you can see, you can tie an arrow with tethered magic with watever spell you want, +1 magnitude to allow for time to fire it, hope it helps 
I assume the caster must also hit as normal with the arrow or javelin? Not a bad idea - Range: Touch is lower than Voice or Sight, for ease of casting and better Penenetration, but you must invest heavily in a ranged weapon ability, to ensure a hit.
Yeah, you must hit with the projectile weapon for the spell to be efective. It´s more or less Base effect +2 magnitudes, (+1 for the duration, +1 for the range), becouse the tether only last as long as the effect, so you can´t cast with this effect durations shorter than Diameter. And you need a Bow roll to aim, so it´s not perfect. However, i think it´s an effective way to do magic Thief-style , without seasons in the lab every time you want new arrows, or the unfortunate case in wich your magic bow is lost.
This thread might be of help:
https://forum.atlas-games.com/t/school-of-owen-bows/4293/1
There are huge rantings on wards there, but some info on bow shooting and associatedf virtues come up to be extremely cool (performance magic, bowshot range, NIall Christie's character, ...)
Cheers,
Xavi
Yup. Tethered Magic is exactly what I'm looking for. I KNEW I had read it somewhere. Thanks for the advice!
I've decided to offer it to the player as a Mystery for him to learn. He'll either find a Mercere Mercurian Mystagogue (try to say that 3 times fast) to teach him the virtue, or he'll learn a new Verditius Minor Inner Mystery that will allow him to tether spells to items, but not to people.
Well IMO, i don't think it's "mystery"-sable because this is a virtue for the mutantes (who have mutantum magic), a branch of the Mercere lineage.
BUT YSMV.
I quite dislike the fact that everything seems to need to be a mystery nowadays. The OoH is becoming so mysterious that it is dull to me. It is no longer a mystery: it seems to be the mainstream evolution path for most magi 
. Everybody and his familiar is part of a mystery cult. or so it seems. After 400-ish years of existence I find it rather weird that all those mystery cults are already cults instead of part of normal hermetic theory or the V&F available to most people.
In the particular case that preoccupies us, I would allow him to take tethered magic as part of his normal training. He is a magical archer after all, so he should have invented his spells with that kind of quirk in the first place. No need for initiation. His tradition teaches that stuff during apprenticeship in order to create a magical archer and not a mage that carries a bow because he fancies it. Deleterious circumstances when not using a bow and favourable circumstances when using it also spring to mind in order to encourage the use of the bow.
If the character is already created, he can learn it as part of an adventure or series of significant adventures. If you want to avoid initiation (in what? A hunter cadre?) it can work perfectly fine.
Cheers,
Xavi
Actually... that was the idea.
To me, there are Mystery Cults -- mysterious, quirky, strange, and exotic. Then there are the various Schools and Paths. Not everything in canon that's written as a mystery falls into the former IMS. Many fall into the latter, and just require a story or two to gain the new knowledge. Some have come into the "mainstream" of hermetic society, others have been kept specifically hidden. Frankly, I probably mis-spoke. I haven't re-read the rules from the core rules on Magi learning supernatural abilities in awhile, and that's probably what I was thinking of.
Player-willing, the character will seek out a Mercurian Mercere, and learn the supernatural ability through a story.
Regarding your criticism, though, The fact that the core rules presents all of these various mystery cults doesn't bother me. I rather like it. During the last 3 years of gaming, there have only been about 2-3 cases where a mystery cult was appropriate for the story, and were thus introduced. Just because they exist doesn't mean we have to use them in our saga. It's all just happy flavoring around the edges.
I see no reason why a bow could not be enchanted like this using vanilla, core rules effects. You just need it to invoke two effects - one a diameter duration version of Watching Ward, and the other the spell to be affected. The bow casts the first when an arrow is nocked and the second when the arrow is released. Since everything needs to be only touch range, the spell levels don't need to be too high which also allows impressive penetrations to be attained.
Watching wards are a ritual spell... can rituals be enchanted into magic items? (serf's parma)
IIRC, no. I remember some conundrum I had in 4th ed. We had a Verditius who was...very efficient. We also ruled (I can't remember if it was a HR or RAW) that any Spell above 10th magnitude was a ritual, just because of size, even if no other parameters demanded it.
And when he put a 11th magnitude effect into an item, I raised the objection. But the 4th ed lab rules clearny state that a ritual spell cannot be duplicated by an item. Our reasoning was then, that only those effects which were rituals because of parameters normally deamding this were prohibited. A 11th+ magbitude effect was allowed.
IDHMBWM but I think 5th ed works the same way. So you cannot make Watching Ward in an item. IMHO.
Watching ward are ritual only because "unnormal" duration.
If duration of the waiting ward is 2minutes (arrow flying), it's not ritual.
And ritual can be put in objects... if they are ritual for another reasons than:
It's remembered in... verditius i think
Testing, Testing ... I replied to this thread earlier, saying more or less this, but it doesn't seem to have appeared. The spell, "Watching Ward" is a ritual, yes, but the guideline doesn't say that that is required, and none of the other ReVi or MuVi metamagics require a ritual. As such, we've always concluded that the special, indefinite duration was what made the spell a ritual (and thus needed a labtext or experimentation to invent).
So, the duration of Watching Ward really is comparable to "Until", since it ways until something specific happens?
Since this does not include Year Duration (per se, although potentially forever), Boundary Target nor Permanency with Creo, it should be perfectly legal for a device. If this is written in HoH/MC-Verditius, I shall have to look it up. Not that I don't believe it - that is the logical place for it to be - but out of curiosity.
Serf's Parma (books home, not read Watching weard in a while...) but IIRC the "weird duration so it is a ritual" justification is in the Watching Ward itself. So "no weird duration = does not need to be a ritual" comes directly from that I think it is not stated as clearly in the watching ward, though, and that this is part of the spell breakdown by components in the base of the spell description.
This whole issue opens a lot of potential for Moon duration watching wards allowing for instant spells carried by grogs.... And for amazing botches when the grog carrying the "grenades" (to put up an example) casually throws the bag carrying the wooden balls enchanted with POF into a cart. FIREWORKS!!! 
That would make the fast items of the natural magicians worse than a magus with watching ward and a good spell repertoire. In half an hour of not very heavy work, a magus can have 50-ish spells ready for his grogs to go out with. Bring a disenchant item as well, though, or you can have quite a mess in one month's time
Cheers,
Xavi
Yes and no. Firstly, you need to have spells of a sensible level to go into the container (and for a nonVim specialist, getting a high level container is nontrivial), and you also need to have relevent spells - anything with a range of voice or sight is pretty useless since the triggering conditions aren't that versatile. So yes, it does allow for some potent combat effects, but also requires that you spend a while inventing sensible spells to use them. A collection of marked rocks and a magus Wielding the Invisible Sling does work nicely though. Botching an attack roll with an arrow set to go off when striking a target is also a poor idea.
As for the disposal - in my last saga, there was a very deep pit behind the covenant. The grogs did not go near it.
The best use of such a thing, however, requires some other Vim spells to hide one's Sigil. Then simply place Moon duration containers on a large number of mice, place large fire spells into the containers and then release them in one's enemies covenant or grain stores. Kidnapped grogs hit with a PeMe spell also work nicely.