Is this homebrew magic item that lets you add your Wisdom modifier to your AC (while attuned) balanced as a rare magic item?

Question

I recently had an idea for a new item in 5e. This item is a cloak that lets you add your Wisdom modifier to your AC (requires attunement). I was thinking of making it a rare magic item, and I was looking for advice.

Is this item overpowered as a rare? Properly balanced? Underpowered? If it is overpowered, what are some changes I can make so it can stay the same rarity and keep its core concept?

The rarity is based on the fact that an amulet of health, which increases the survivability of non health-based classes a lot, is rare. The amulet of health also only needs to be worn on the neck, while this cloak has to be worn in place of armor, an extremely common item to find enchantments on. Another item that adds the same amount of AC (overall) is a +3 shield, which is very rare; however, that takes up an uncommon slot, the shield slot, so I think the cloak is sufficiently less powerful to decrease the rarity. I am looking for advice on changes to make if this item is overpowered, not to scrap the idea entirely.

Note: I have made a less powerful item that is designed based of advice from this question. I am asking for advice on balance here.

Answer 1

On Bounded Accuracy and Armor Class

Before attempting to judge the item, it is important to first understand AC (Armor Class), and the effect of AC on play.

AC is the "threshold" to which AR (Attack Roll) are compared to, therefore any discussion about AC must be calibrated by the distribution of AR values of the opponents of the creature, so as to be able to determine the chances that said opponents will hit or miss.

Distributions are complicated, so I like to look close to the extreme for a quick ballpark: how will it play at level 20?

Heavy hitters sample:

• +14: Fighter level 20, with 20 Strength and a +3 Weapon.
• +16: Barbarian level 20, with 24 Strength and a +3 Weapon.
• +16: Monster CR 20+ with 30 Strength.

There are (rare) ways to get better AR bonuses -- using miscellaneous bonuses -- but those are close to the top AR bonuses that anyone will ever face.¹

From there, we can determine the chances to hit for a number of ACs, though I'll reverse it to determine the target AC for a few set chances to hit.

Let's assume the opponent is the Fighter (+14), without Advantage:

Chance to Hit	Die Roll	Max Target AC
75%	6+	20
50%	11+	25
25%	16+	30

So, if you want the Fighter (+14) to hit 50% of the time (ie, on a roll of 11+), then the opponent must have an AC of at most 25.

¹ Why are the AR bonuses so "fixed"? Because of Bounded Accuracy, which vastly reduced the dynamic range of all roll modifiers. See questions such as Why is Bounded Accuracy called Bounded Accuracy? for more information on Bounded Accuracy itself, and the problems it aimed to solve.

Evaluating the Item

From there, in order to evaluate our item, we need to evaluate whether it "breaks" the typical range of AC values. As a DM, you may be in position to prevent the breakage, of course, however the more potential for abuse, and the more intervention needed, the less balanced the item itself is.

The Monk

The Monk has the following first-level feature:

Unarmored Defense

Beginning at 1st level, while you are wearing no armor and not wielding a shield, your AC equals 10 + your Dexterity modifier + your Wisdom modifier.

Which may be combined with the following item:

Bracers of Defense

While wearing these bracers, you gain a +2 bonus to AC if you are wearing no armor and using no Shield.

An optimized Monk is likely to have reached 20 Dexterity and 20 Wisdom by level 20, so they would be looking at an AC of 22 with the Bracers, which is still reasonable as per our computations above.

If instead of the Bracers they use the cloak, they immediately get an AC of 25, and if they add the Bracers, an AC of 27.

For a permanent AC -- not the result of a short-term buff -- this is very strong. Furthermore short-term buffs can bolster it temporarily.

The Cleric, the Druid, and the Ranger

With a single 1-level dip into Monk, any of those characters can pull the same shenanigans, and being Wisdom-based, they have little opportunity cost for doing so.

The Martial Classes

The typical formulas for martial classes ACs are:

• Light Armor: 12 + Dexterity Modifier, maxes out at 17, or 20 (+3)
• Medium Armor: up to 15 + min(2, Dexterity Modifier), maxes out at 17 or 20 (+3).
• Heavy Armor: up to 18 or 21 (+3).

Replacing the armor with your cloak, supposing the character has a Wisdom of 20 otherwise why bother, allows the character to reach an AC of 20.

The cloak is thus equivalent to a Light Armor +3 or Medium Armor +3 in terms of power for those characters.

Judgement: This item is Very Powerful, it may easily equal +3 armors, and with the cost of a single level Monk-dip straight eclipse them.

Recommendations

As has been seen with the Monk, and assorted Wisdom-based casters, a straight bonus to AC is dangerous for balance.

This is the reason that there are 3 class of items granting AC in 5e:

• Armor give an AC formula.
• Shield give a good AC bonus (+2 to +5), at the cost of an occupied hand.
• Miscellaneous items give a small AC bonus (+1 to +3), at the cost of Attunement.

Since your cloak replaces an armor, it should give an AC formula.

For example, your cloak could give an AC of 12 + Wisdom Modifier as an Uncommon Item, and rise all the way to an AC of 15 + Wisdom Modifier as a Legendary Item, matching a Light Armor AC calculation.

Answer 2

It is unbalanced at any rarity.

An item that adjusts your AC between -5 to +10 fundamentally breaks the amount of AC that a single magic item may provide up to +3 - read about bounded accuracy. An effect like this would be similar to a bread and butter class features of a hypothetical class — if you want to hand it out despite that, any rarity below artefact rarity would be inappropriate power-wise.

You might also want to read What is the highest possible AC? to get an understanding about how optimised AC values function.

A simple fix would be to re-fashion an item with a fixed modifier between +1 to +3 and use flavour text or a prerequisite that fits the player you plan as the beneficiary.

Answer 3

This item is probably overpowered. Compare the very similiar Bracers of Defense which give a flat +2 bonus if you're not wearing armor or using a shield; they are also Rare.

This item could go up to +5 (and probably will, since it'll go to whomever has the highest Wisdom) with less stringent restrictions (since you can use it with a Shield)

It also allows Monks (the most common user, I guess) to add twice their Wisdom bonus to AC, along with their Dex, which is going to make their AC very high. (20 from max Wis alone, plus whatever their Dex is)

(Running on the assumption you can't combine this with armor. If you can, it becomes way better, better than +3 Armor, which is already Legendary)

Answer 4

If this can be worn by Monks without disabling their Unarmored Defence, this item is equal to +5 Bracers of Defence, which would be beyond Legendary. However, this problem is solved if you add a limitation that wearing it counts as wearing armor, which is stronger than your current statement that it is worn instead of armor.

Then it does nothing for a Monk's AC. For Druids and Clerics, expected to reach WIS 20, it becomes equivalent of +3 Studded Leather Armor for AC 15, because it allows full DEX bonus to be added. That has rarity of Legendary.

For a Wizard it would be inferior to Robe of the Archmagi, which provides AC 15 and a bunch of other benefits. That item is also Legendary.

It could be argued that having WIS 20 or even WIS 18 is rare enough, that it would be more fair to consider your item to have just AC 14, making it equivalent of Studded Leather +2 on average, which is Very Rare. It is also much less powerful than the Robe of the Archmagi, which supports lowering the rarity.

A Druid might reach the same AC with Dragon Scale Mail (unless they have high DEX), which as also other benefits, but also stealth disadvantage, and is Very Rare. I think any Druid or Cleric would choose Dragon Scale Mail over this item almost always, which hints that lower rarity than this might be ok.

Having it as rare as Studded Leather +1 (AC 13), which is Rare, seems to understate its flexibility and uniqueness. It is better to evaluate it for the "best case".

For a Cleric without high Dexterity it's pretty much equivalent of Breastplate +1, which is also Rare, but again this item is much more flexible, and able to reach higher AC with DEX, so making it more rare than this seems reasonable.

Conclusion: It should be Very Rare. A case could be made for it to be just Rare.

Answer 5

If the cloak is worn instead of armour, as you mention in your post, then it seems to me that it's in line with the Monks "Unarmoured Defence" ability. In this case, I'd say it's not OP.