The Magic Mouth spell allows the caster to store a message within an object. One of my players asked me to define a message as he wanted to store a captured monster's roar as evidence, so I dictated that the spell could hold and recite any audible noise provided it was not more than 25 distinct noises and did not exceed the 10-minute mark as specified in the spell. This seemed reasonable to me until he asked to store a shatter spell. Shatter is a spell that when cast emits "A sudden loud ringing noise" that will damage nearby creatures and objects. Because the effects of the spell are entirely vocal, could you store a shatter spell inside a magic mouth, and if not, to what extent can you store no-traditional messages such as monster noises and other audible cues that don't specifically convey any message?
Can you store a Shatter spell in a magic mouth
dnd-5espells
Related Solutions
No.
PHB, pg 203
If you can't provide one or more of a spell's components, you are unable to cast the spell.
When you cast Magic Mouth you are embedding a message in a usually mundane object to be spoken at another time. It is physically the object that speaks the words. Since you are not providing the spell's components, you are unable to cast the spell.
RAW
Rings of spell storing capture a given levels worth of spells. Cantrips are considered level 0, so by RAW they couldn't be stored.
Any creature can cast a spell of 1st through 5th level into the ring. (DMG, p. 192)
Why not?
If you could, you would be able to store an infinite amout of them in the ring and pass it off to another party member, essentially giving them a free set of off-class cantrips.
The level of the slot used to cast the spell determines how much space it uses.
A pure fighter with an endless supply of free eldritch blasts, green flame blades or chill touches would be game breaking.
Houserule and the Problems it Might Cause
A DM might rule that for the ring of spell storing purposes the cantrip is a level 1 spell.
Which might still break balance. Because cantrips are "free" attacks (in that they don't spend resources) some of them are designed to be the primary attack of certain classes. A level 2 fighter for instance, who convinced a high level warlock into storing for him, could use Action Surge to fire 4 beams of Eldritch Blast from the ring of storage, then fire 4 more beams of Eldritch Blast. Each blast potentially doing 1d10+(CHA modifer of warlock) damage and pushing the target back 10ft -- if the invocations used at the time the Warlock stored the spells could be released.
Granted, multiclassing could (possibly) allow you to do that, but that has been balanced and play tested and has costs. It would be odd for a level 2 fighter to be in the same party as a level 11 Warlock, so it isn't likely something that would happen alot, just that it could if the the player met an NPC or such willing to store the spell for him.
For prestidigitation, I don't see a problem with a DM letting you use a Ring of Spell Storing counting it as a first level spell.
Could one just create a Ring of Prestidigitation some other way?
Yes. And at a fairly reasonable price you could either craft (if your DM allows crafting) or buy it. That said, if magic is more rare in your world the costs for making or buying it could vary.
Crafting it.
The cost for buying a Common Item is 50 gp to 100 gp , and the cost for buying a Uncommon Item is 101 gp to 500 gp (DMG p 135). Crafting rules state that "you must expend raw materials worth half the total market value." (PH p.187).
It would take 4 full days and about 50 GP if the DM says it is a Common item, or 20 days and about 250 GP if it is an Uncommon item.
The chart in the DMG (p. 129) seems to say that to craft a magical item you have to spend the total cost of the item and the time. Running completely RAW for magic items would put it at 4 full days and about 100 gp for Common item, or 20 days and about 500 gp for Uncommon item. The one issue with this is that there is no benefit to spending the time on crafting over just buying it. I assume the reason that this is the case in the rules is because previous editions allowed wizards to get get very rich selling magical things.
Buying it
If the DM allows you to find a place the sells it, the purchase price should be somewhere between 50 (if it common) or 500 (if it is uncommon).
Best Answer
Magic mouth cannot be used to record anything except for the sound of your own voice speaking words.
Magic mouth defines "message" for us:
Non-descript noises, grunts, growls, sonic booms, and the sound of a shatter spell are not words, so are not eligible for storage in a magic mouth.
Further, magic mouth states:
Magic mouth cannot be used to record anything except for the sound of your own voice speaking words, and doesn't produce any sound except the sound of your own voice, speaking those words, exactly as you recited them when you cast the spell.