What rarity is appropriate for a homebrew item that lets a Wizard delay declaring a single spell preparation?

Question

Consider the following homebrew magic item:

Uncanny Bookmark

Wizard only, requires attunement.

When you complete a long rest, you may optionally delay choosing the spell for one of your spell preparations. At any point while this spell preparation remains unchosen, you may choose a spell in your spell book that you could have prepared during the long rest and declare that this spell is the spell that you prepared. This choice may be made at any time, and it does not require an action or reaction. Once a spell has been chosen for the delayed preparation, the preparation becomes permanent until you complete a long rest.

What is the appropriate rarity for such an item?

My intuition is that this item bears some similarity to a wish spell, in that both allow you to cast any spell in your spell book. This clearly isn't a perfect comparison, but it suggests that the item might need to be as rare as Legendary (per the DMG's Magic Item Power by Rarity table on p. 285).

Answer 1

This would work best as a Rare item, but test

This is an item that would not be unbalanced in tier one. It naturally scales its power down because early on, the selection the wizard has access to is so much smaller. For example, for a 1st level wizard with Intelligence 15 and two rituals like detect magic or comprehend languages already can cast all the spells in their spellbook. All this would do is allow them to cast the rituals as normal spells. It gets more powerful as the wizard gets more powerful. And I think what level of play the item works well with with is a useful consideration for rarity assignment.

There is little that directly compares which makes power assessment difficult. However, there is guidance in the DMG that rarity should be based on spell level for an item that can create a spell like effect. So I'm looking at this through the lense: if this where a spell, what level would it be?

As @TheBlest pointed out in the comments (now unfortunately removed), the UA playtest contains a spell that has a very similar effect, Memorize Spell, which allows you to memorize any spell from your spellbook in exchange for an appropriate slot memorized spell. That spell is pegged as third level. There is one large difference: your effect is instantaneous, not even requiring a reaction, while that spell takes a minute to cast, so it is useless in combat. This makes your effect more powerful.

On the other hand, wish this ain't. Wish allows you to cast any spell up to 8th level, from any list, and without any material components. Here you are still limited to the effects you already have access to, and by all the normal costs, plus you cannot create new effects. That is a huge step down in power.

If lateral transfer from a similar system is allowed, I can add from my play experience: in Pathfinder (which plays similar to D&D 3.5) wizards have a feature called Arcane Bond that allows them to cast any spell in their spellbook once a day, and that was nice to have, but not super powerful.

Attunement cost

In addition, this consumes one of your precious attunement slots, while a ring of three wishes does not. That is a large cost. When I first saw this, I thought, I don't really care what rarity this is, the question is would I give up one attunement slot for being able to have one flexible pick like this? Flexibility certainly has its own power, but it is much harder to quantify than additional spell slots and spell levels. You could use that attunement slot for other items like a staff or wand that give you not only options but also raw firepower in the form of many additional castings.

From practical play, there always is a situation where you wish you had memorized the knock, or the charm person. However, for the lower level spells of first or second level, you can quite effectively also address this by crafting Uncommon scrolls, and that costs no attunement.

So, an item that can replicate a 3rd level effect like Memorize Spell, could be Uncommon, but this effect would be more powerful due to its speed. An item one step down from level 9 spells like wish would be Very Rare.

I think this would work best as a Rare item, so you could actually still get to use it during a normal campaign for some time, possibly getting access to it as early as 5th level. Very rare items typically only get handed out from level 11 (Xanathar's, p. 135), when many published campaigns are already winding down.

Because this is such an unique effect that is hard to triangulate for power, I would strongly recommend to test this, and be prepared (and prepare your players) to adjust if it turns out to be more powerful than you thought.

Answer 2

I'd consider adding a level limit, then attaching a rarity to that level limit.

Second, as an attunement slot, we can justify more than just flexibility but a tiny power bump in order to simplify its wording.

Uncanny Bookmark

Requires attunement by a Wizard

When attuned to this bookmark, you may choose to cast a Wizard spell in your spellbook that you do not have prepared of up to 2nd level without expending a spell slot. You cannot use this item to cast a Wizard spell you would not be able to prepare. Once you have done so, this spell is considered prepared for you until you complete a long rest or lose attunement to this bookmark, and you cannot do so again until you complete a long rest.

Rarity: Uncommon (2nd level), Rare (4th level), Very Rare (6th level), Legendary (8th level).

This gives a small power boost (in the form of an extra slot) to make up for the attunement. It is otherwise thematically identical. Unlike the base item it doesn't auto-scale in power at higher levels; a high level wizard can't use a heroic tier item to suddenly cast wish.

It is limited to level 8 spells, keeping the uniqueness of 9th level spells as 1 per long rest.

Removing the "without using a spell slot" makes it a significantly worse item, but also a less fun one. I might drop the rarity by 1 tier?

Requires attunement by a Wizard

When attuned to this bookmark, you may choose to prepare a Wizard spell in your spellbook that you do not have prepared of up to 2nd level. You cannot use this item to prepare a Wizard spell you would not be able to prepare. Once you have done so, this spell is considered prepared for you until you complete a long rest or lose attunement to this bookmark, and is in addition to the spells you prepared normally, and you cannot do so again until you complete a long rest.

Rarity: Common (2nd level), Uncommon (4th level), Rare (6th level), Very Rare (8th level).

Items with a variety of level limits are common in 5e - most items with a +1 through +3 bonus follow this pattern. Scrolls and Tattoo's and Spell Gems also vary in rarity based on the level of the spell they support.

The bookmark written above is similar to a Spell Gem from Out of the Abyss; the Gem has a few more abusable corner use cases, but the Bookmark is more flexible.

Answer 3

Legendary

When trying to understand the power of a homebrew choice, you need to look at both the "intended" consequence, and the extreme.

As pointed out in the comments, this works very similar to the wish spell:

The basic use of this spell is to duplicate any other spell of 8th level or lower. You don't need to meet any requirements in that spell, including costly components. The spell simply takes effect.

But there are two major difference that are a pro and a con:

1. Using this bookmark, presumably, still requires any components needed by the spell. So you cannot simply make a Simulacrum on a whim.
2. You can instantly cast a non-prepared 9th level spell.

It gets more powerful the higher the level of play

At 5th level, a wizard can memorize 5 + your Int modifier (we'll assume 18 at this level) for a total of 9 spells prepared. A wizard can prepare 8 of any level spell. The smart choice is to actually not memorize a 1st level spell of little use, like say, don't get charm person and fill up on the higher level spells like normal. The chance of the character needing charm person during a day is small. But the bookmark doesn't care about what spell level is "missing". And when the time comes, you can cast a different 3rd level spell (so long as you still have a spell slot). So prepare fireball and hypnotic pattern, because you can also cast haste if the need arises.

Now consider the wish spell. Its power comes from being able to cast ANY spell of 8th level or less. It is extremely powerful to have memorized. But there are only a few 9th level spells, and they are all pretty good. However weigh that against having only a single 9th level spell slots at 20th level.

But because you didn't memorize that 1st level charm person, you can forget about memorizing wish and grab other 9th level spells. And when the time comes, swap in the wish spell to cast any other 8th level or lower spell. Even spells not in your spell book.

Comparison

The ring of three wishes is a legendary item. Since this item can be used very similarly, I would put it at the same rarity.

The differences are:

1. The ring works three times, then it is gone. Whereas the bookmark resets every day.
2. The ring can cast any spell automatically, but the bookmark requires the spell to be in the wizard's spell book. But once the wizard knows wish, then it's identical.
3. The ring allows the wearer to cast wish three times total without using spell slots. The bookmark would allow wish to be cast twice a day maximum (the two spell slots).

Answer 4

It should be at least legendary.

There is a bunch of official items from Tasha's Cauldron of Everything that work in a similar way of the proposed item: Alchemical Compendium, Astromancy Archive, Atlas of Endless Horizons, Duplicitous Manuscript, Libram of Souls and Flesh.

All of them have 3 charges, and they share a common option:

If you spend 1 minute studying the book, you can expend 1 charge to replace one of your prepared wizard spells with a different spell in the book. The new spell must be of the [X] school.

The sole difference is the school to which the new spell must belong to, which is thematically linked to nature of the item. Each one present another option (that costs 2 charges) linked again to the theme of the item. These items are listed as Rare.

Since they are providing a similar mechanic to the proposed item, one has to compare the aspects that look alike:

1. The substitution option can be taken 3 times per day, in ideal conditions (3 charges left).
2. The new spell must belongs to a particular school of magic.
3. The change takes 1 minute.
4. The wizard does not have to leave out one slot from the prepared spell list.

The proposed one instead:

1. The substitution can be taken once per long rest.
2. The new spell can be any in the spellbook.
3. The substitution is instantaneous and does not require an action, a reaction or a bonus action.
4. The wizard has to leave one slot from the prepared spells list free.

There are two aspects that seems to set the power of the Uncanny Book at a lower level than the spellbooks from Tasha's, namely 1) and 4), but the other twos allow the wizard to be incredibly versatile, since just with a thought they can choose any spell from the spellbook that may save their life, solve a problematic situation, or whatever hard situation that they may encounter.

There is another magic item that provides a similar option, the Crystalline Chronicle:

• If you spend 1 minute studying the information within the crystal, you can expend 1 charge to replace one of your prepared wizard spells with a different spell in the crystal.
• When you cast a wizard spell, you can expend 1 charge to cast the spell without verbal, somatic, or material components of up to 100 gp value.

The first bullet allows the change of prepared spell, without leaving out a prepared slot and without any limitation on the school. Anyway, it still requires 1 minute for the change. The rarity of this is Very Rare.

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Even in the first tiers of play the Uncanny Book could be a game changer. For example, a 4 level wizard has 12 spells in the spellbook (by following the rules in the PHB and without considering additional spells provided during the adventures by the DM). They can prepare a maximum of 8 spells, supposing that they maximized the INT score. Using this item, the wizard can prepare 7 spells, choosing to leave out some that may of some use in particular situations, for example the Shield spell, since they know they always managed to be out of the fight, or the Mind Spike because they are not planning to read thoughts. But by using this item they have the whole spellbook at their disposal in an instant, being hence ready to adapt to a large range of situations.

This further versatility to the Wizard class makes the Uncanny Book's rarity (strictly) greater than the rarity of one of the items from Tasha's: it elevates the rarity of the Uncanny Book to Legendary, not even Very Rare, even comparing it with the Crystalline Chronicle, since the latter requires 1 whole minute for the changing.

Actually, there is another item in the DMG, the Tome of the Stilled Tongue, a legendary item providing (again) a similar option for casters:

If you can attune to this item, you can use it as a spellbook and an arcane focus. In addition, while holding the tome, you can use a bonus action to cast a spell you have written in this tome, without expending a spell slot or using any verbal or somatic components. Once used, this property of the tome can't be used again until the next dawn.

In order to cast any spell in the spellbook, this item requires to use a bonus action but the caster does not spend a spell slot, while the Uncanny Bookmark allows to do this using an Action (the Cast a Spell action) but at the cost of leaving one "preparation slot" free. The provided feature (casting any spell in the book) is the same, but the Uncanny Bookmark has a slightly higher cost (leaving a "preparation slot" free), which is not so impactful, due to the high number of spells one can prepare. Supposing that the DM is not very generous, a 20th level wizard has 24 spells in their spellbook and they may prepare 25 spells, provided they maximized their INT score. The cost is hence negligible.

The real power of both items lies in being able to cast an unprepared spell: but the Tome allows to do this per day, while the Uncanny Bookmark allows to have that spell prepared until the rest of the day, hence the wizard can cast it multiple times, provided that they have slots available.

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From a game balancing point of view, we have to remember that the 5th edition of Dungeons and Dragons is highly in favor of the players, and the wizard class is really powerful and very versatile. Using this item augments the power and the versatility of such class, against other classes, and further eases the game, allowing the wizard to access and to use spells in their whole spellbook in an instant.

To be honest, I do not think that I would use this item in my games as a DM: I could give it a try in case I consider this as an artifact designed for wizards that, among other properties, presents this option for delayed spell preparation.

Otherwise, since there is already a magical item that provides a very similar option to what yours item does, I suggest to use the Crystalline Chronicle.

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