Say you're a wizard or sorcerer who wants to make a Ring of Protection. You can't prepare/know Shield of Faith, but you can use Limited Wish. Does this satisfy the requirement, or do you HAVE to have the specific spell in order to craft an item with that spell?
The rules don't specifically cover this use of limited wish, but they suggest that a reasonable DM should allow this.
According to the rules on Creating Magic Items:
These prerequisites must be met for the item to be created. Most of the time, they take the form of spells that must be known by the item’s creator (although access through another magic item or spellcaster is allowed).
And you need to effectively cast or trigger the spell effect each day:
The act of working on the armor triggers the prepared spells, making them unavailable for casting during each day of the armor’s creation. (That is, those spell slots are expended from his currently prepared spells, just as if they had been cast.)
In other words, there are three defined ways to meet spell prerequisites:
- The crafter knows the spell
- The crafter has a magic item which duplicates the spell
- Another caster knows the spell is available to help
That second one is important, because activating a magic items is explicitly described as "duplicating" the spell, not casting it. Rules Compendium, p.84:
Activating a command item takes the same amount of time as the casting time of the spell that the item's power duplicates. If the power doesn't duplicate a spell, activating the item is a standard action unless its description says otherwise.
"Duplicating" is the same terminology that limited wish uses. In other words, while limited wish technically does not allow you to "cast" shield of faith, it can allow you to duplicate the spell. The magic item creation rules quoted above do not at any point require you to "cast" the spell, but do allow you to provide it via items which duplicate it.
Now, this is not explicit, because we're still talking about two similar but different things: duplicating a spell with an item, and duplicating a spell with a spell. However, the manner in which ambiguous D&D rules are adjudicated by the DM is described on Dungeon Master's Guide p.6, which explicitly recommends that DM allow inferences from similar rules:
Look to any similar situation that is covered by a rulebook. Try to extrapolate from what you see presented there and apply it to the current circumstance.
It would be a very reasonable inference, therefore, to allow limited wish to duplicate a spell to craft an item. However, it is technically still the DM's call, rather than something that the rules explicitly allow.
Yes, this works.
Yes, using wish for this works - and yes, you don't need to "have" the spell for it to work if you find another source to cast it.
The description of wish states:
A wish can produce any one of the following effects:
- Create a magic item, or add to the powers of an existing magic item
Material Component: When a wish duplicates a spell with a material component that costs more than 10,000 gp, you must provide that component.
XP Cost: The minimum XP cost for casting wish is 5,000 XP. When a wish duplicates a spell that has an XP cost, you must pay 5,000 XP or that cost, whichever is more. When a wish creates or improves a magic item, you must pay twice the normal XP cost for crafting or improving the item, plus an additional 5,000 XP.
If you use wish/limited wish for the prerequisite for creating a magic item (to copy the spell you don't have):
Note that all items have prerequisites in their descriptions. These prerequisites must be met for the item to be created. Most of the time, they take the form of spells that must be known by the item's creator (although access through another magic item or spellcaster is allowed).
I also found this in the DMG p.215
A spell prerequisite may be provided by a character who has prepared the spell (or who knows the spell, in the case of a sorcerer or bard), or through the use of a spell completion or spell trigger magic item or a spell-like ability that produces the desired spell effect
So we can assume only the spell effect is required, so limited wish/wish works that way.
(You could argue wish is neither a spellcaster nor an item, but what about an item that could cast wish? It is a magic item, after all - but if your DM rules it out, find another item/spellcaster instead.)
Wizards and sorcerers
For a wizard, I'd suggest just learning the spell you need, buying a scroll to learn it, or asking for help from another spellcaster - because though this would work, it would be a waste of resources because you need to "consume" a spell each day of crafting, and wish/limited wish are very expensive.
So you could use limited wish to scribe a scroll instead of casting limited wish every day to do so if you have the feat. From the rules on creating rings:
The act of working on the ring triggers the prepared spells, making them unavailable for casting during each day of the ring's creation. (That is, those spell slots are expended from his currently prepared spells, just as if they had been cast.)
For the sorcerer: Either buy a knowstone if such a thing is allowed, or craft the magic item you need with the help of someone knowing the spell or use a wand/staff/scrolls if you have enough to craft.