What level should a spell that lets a character briefly attune to an extra item be?

Question

I am considering adding a homebrew spell to a game I DM. Here is the exact wording I intend to use:

Superior Attunement

8th level transmutation

Casting Time: 1 action

Range: Touch

Components: V, S, M*

Duration: 8 hours

You touch one creature and one magical item which requires attunement, but to which no creature is currently attuned. At any time within the next eight hours, the affected creature may, as a bonus action, touch the affected item and instantly attune to it without requiring an attunement slot. The creature remains attuned to the item for one minute. After one minute, the spell and the attunement end.

The spell ends early if the creature falls unconscious or if any creature attunes to the magical item. No creature can use this spell to attune to any more than one item at a time.

The creature must still meet any specific requirements this item has for attunement (class, alignment, etc.). If a creature attempts to use this spell to attune to an item whose requirements it does not meet, it suffers the same consequences as it would in the normal attunement process.

* (Any magical item that requires attunement, but to which no creature is currently attuned)

I have tentatively decided this spell should be an 8th-level spell. I feel this strikes a good balance. This spell is a utility spell, and who wants a 9th-level utility spell? But it has the potential to make a character quite powerful for a short period of time, so I don't want a character to be able to cast it more than once a day.

Does this seem like a reasonable spell level? If not, what level should this spell be

Answer 1

It is probably okay to implement

We actually do have reference for just how powerful a fourth attunement slot can be by way of Unearthed Arcana. The Artificer has this ability at level 5:

Your superior understanding of magic items allows you to master their use. You can now attune to up to four, rather than three, magic items at a time.

While Unearthed Arcana is not inherently balanced, in my experience with players using the class, the extra attunement slot is not that meaningful. Even when the artificers get a fifth slot at 15th level it didn't make the game feel too unbalanced.

Keep in mind, as usual with Unearthed Arcana, that there may be balance concerns in general. Since the Artificer has yet to be released officially, any of its features could be changed if that occurs. We have had multiple books released since the Artficier appeared in Unearthed Arcana so it almost certainly requires some changing in response to feedback.

However...

This is heavily contingent on the weak nature of the Artificer class when it comes to their other features. The fact that the spell can be cast on any ally means you can achieve much more effective use of attunement slots. I would exercise caution in using this spell in a campaign with too many magic items that interact well together (or in a world where magic items can be bought). I'm sure there are some groupings of magic items that could become unbalanced with other class features (such as stacking lots of AC bonuses).

What level of spell?

Judging by its place in the artificers level table, I would put it at 5th or 6th level. Haste is a 3rd level spell that simulates a 5th level feature: Extra Attack. However, haste requires Concentration, which is a severe cost, and has a very small duration. Removing concentration adds about 1-2 spell levels and the flexibility to activate the attunement any time in 8 hours adds 1 level. I came to this conclusion by looking at the effect of casting At Higher Levels for bestow curse (another 3rd level spell):

If you cast this spell using a 4th level slot, the possible duration is extended to 10 minutes. If you use a 5th or 6th level slot, the duration is 8 hours. If you use a 7th or 8th level slot, the duration is 24 hours. If you use a 9th level slot, the spell lasts until it is dispelled. Using a spell slot of 5th level or higher grants a duration that doesn't require concentration.

If you want to play it super safe and/or magic items are more readily available or more selective (such as through buying and selling for good combos) than is standard for 5e, then 7th or 8th level makes sense.

Answer 2

No, that's not going to cause major balance issues. Common homebrew alterations do far more.

There are several major reasons for the limitation- some items are overpowered, and a surplus causes balance issues. Too many magical items gives you too many complicated options and slows the game down. It stops bonuses from getting out of hand.

Lets review some of the common ways this is homebrewed. A lot of people chafe at the three item limit, and many methods have been devised to bypass it.

1. Tie magical items to proficiency bonus. Commonly people tie how many items you can attune to to your proficiency bonus. Your spell isn't going to increase their attunement to a level above this, so it's fine.

2. Grant an extra slot as an epic boon. They gain your spell slightly before this.

3. Let players not need attunement to items that don't cause balance issues. This is much weaker than this.

4. Let players use a feat to purchase an extra attunement slot. This is weaker than this.

5. Make homebrew magical items that don't need attunement. This is common.

So, for all of the varied methods people have used to avoid the limit, yours is notably weaker. The main issue isn't the three item limit, generally- it's which items you combo as a player. It's much weaker than the common homebrew adjustments.

Here's an example of an item that can cause serious balance issues, as it breaches bounded accuracy- a belt of giant strength, which boosts strength. A previous player here complained about how it made them feel far less useful.

By contrast, while this item also requires attunement it's much much weaker. On a roll of 20, it does 3d6 extra damage and heals you, so around 0.5 extra damage per hit, on average- not especially potent.

Here's another example of an item that requires attunement. A helm of telepathy with a DC of 13. That's not a hard DC to make. Wearing it isn't going to screw up the balance of the game that much.

The power of magical items and working out who gets what is much more important than the exact number often.

From personal experience, I've had players use a single magical item to overshadow others, ones that heavily boosted attack powers or skill powers which should have been in other's domains, and had players use six magical items simultaneously without many balance issues because they didn't pick stat boosting ones. Whether the items break bounded accuracy or allow someone else to surpass another party member in a key area has been the main issue.