Outside of a device, using a watching ward, or other ritual
Is it possible to have an effect auto re-trigger itself over the duration of the spell?
For example Moment effect retriggers and goes off for X rounds. with X permanent effects.
My instinct is no, as extending a moment effect means the one effect lasts till the new duration and then resets to "Normal" without any permanent effect.
But I do remember seeing something in one of the Core 40 around this, but I can't for the life of me find it.
Not knowing what OP had in mind, I think it is a bit unfortunate that the watching wards only makes a one off trap. Setting up a lab, it would be nice if one could make permanent trap, which keeps triggering the same spell on every intruder.
Now watching ward has a special duration, which makes it unique. If you tried to make a repeating watching ward, it would be limited to regular durations, which means maximum a year. Permanent rituals were removed from 4ed to 5ed.
I think it should be possible to make a watching ward-like effect with a one-year duration, which does trigger the same spell over and over again on the same condition, but with the vis cost and the limited duration, I do not think it is going to be very popular.
What the player is looking for is something that is going to be used in combat, that will damage an opponent in a moment and then repeat the effect without recasting the spell, maybe for several rounds.
A device can do this easily.
But in this case, they are looking for a spell. Being in a combat situation means the rituals are out anyway.
This could be done with a "While they are being attacked" condition, but I think they are after something simpler.
That would depend on the effect. A Cloak of Fire that damages anyone that attacks you in combat. But there's no way to design every spell to activate when you're being attacked except by enchanting a device.
You can create ongoing situations that keep causing damage. There are many canonical examples of that, like the Coat of Flame that two mentioned above. There are a bunch more examples even in the core book. But you can't usually get a repeating effect like this. Alternatively, you could be something like surrounded by flames yourself so that it's ongoing, but only if the opponent is close enough to attack you, so it behaves somewhere in between ongoing and repeated.
Spells with Container Targets (ArMDE 09-Spells) can be configured to affect targets entering them after casting, while their Duration lasts. That can also be used to attack targets blundering into the Container after casting.
Right. You cannot make a repeating spell. What you can do, as others also suggest, is to make a spell which either sustains an effect with a duration or creates an effect which sustains itself naturally. Fire is the most obvious medium to work this way, and can be made to burn either magically or naturally (if there be ignitable fuel), but it is not the only possibly medium.
Then there is the room and circle cases which was mentioned, but possibly difficult to use effectively.
So the key logic is the effect that can naturally envelop or sustain itself, such as fire, a pool of water, the shadows in a room etc, all these being environmental conditions. Being sustaining make them repeat, stop the sustaining effect, and the spell can repeat as it can't sustain.
So extending this "design" principle you should be able to replace the damage effect with say a Demon’s Eternal Oblivion effect as long as it has a sustaining aspect.
Because I don’t see it mentioned here the Merinita Mystery of Spell timing also allows:
In addition, this Mystery allows the Merinita's spells to have recurring effects. Such spells are designed so that from their casting onward, they always trigger in response to an environmental or physical condition, increasing its level as described on the chart below. A recurring spell must be cast as a ritual, and effects that require a ritual because of their unusual effects or non-Hermetic origins (not because of their level or spell parameters) cannot recur. For example, a ritual with Year duration can be made to recur, but a last-ing effect like Chirurgeon's Healing Touch (CrCo20) or a unique effect like Breath of the Open Sky (ReAu40) cannot.
Keep reading the description after the conditional durations that were originally mentioned. Page 101 of HoH:MC
I like the concept of the +1, but I would debate on the duration, I guess it is presented that way because we have no 2.5 hour duration (7 miles walking time)
I remember this having come up in some saga, and I don't think we reached a consensus, or at least not one single, obviously correct interpretation.
IIRC the case at hand was my rusticanus learning rope making. He hired a craftsman in game to train him for a season or two with an express promise never to make a competing business. No problem with the restriction, since he wanted to make ropes as charged items, which could be laid out in a closed circle, triggering a circle/ring effect when the circle is closed in a tied knot.
One of the spells he planned was a circle/ring variant of Demon's Eternal Oblivion. IIRC the troupe voted down the idea of a repeating effect, draining might every round for the duration, and I think he ended up with a momentary effect, draining might only, but from every demon within the circle.
The background urging him to learn this trick at the time was an anticipated attack at the wedding of a friendly noble. The neat trick about circle spells is that you do not have to sense the demon. You only have to sense the circle to affect every demon inside. Thus even the momentary spell is a huge benefit. The rusticani rope means that you can safely make a 300' rope and enclose the entire church. Or at least, that was how we reasoned. We may have pushed the limits for charged items and circle spells.
But I digress. The point I wanted to make was that I have not seen a compelling case that repeated drain to beings inside the circle is or is not allowed by the rules.
In the end, it never came up in play, because we jumped the gun and had to fight the demon lords in open battle instead.
What is clear, I think, is that such a sustained effect would apply every time the demon enters the circle, if they can enter without breaking the circle. So then you only have to lure the demon into and out of the circle.
You should look at the description of the spell too. It is a research spell for which the Magi won the prize of the house as the greatest innovation of the last 7 years.
Ain't just a +1 that will do it.... unless you want it to.
My point was not "This is how you do it" but rather that there are published examples, including one in the Core book. It has already been done, individually we just have to determine how hard we want it to be in our individual Saga.