How do you distinguish between magic effects that bypass immunity and those that don't?

Question

This question was triggered by a question with respect to punching with Ogre Gauntlets and counting the unarmed attack as a magical attack for purposes of bypassing immunity.

Basically, it goes like this: If you have a weapon with a certain magical effect, let's say the minor property unbreakable (can not be broken, requires special means) or temperate (no harm in temperatures between -20 to 120 F), it can bypass the immunity of something like a Werewolf because it is magical instead of mundane. This goes for any minor property because those properties are under the Magic Items portion of the DMG on pg.143.

How does this differ from a pair of gauntlets with the exact same effect being used as an improvised weapon (emphasis added for clarity) from dealing damage in the same manner to the same Werewolf? Or something that's clearly not a weapon like a Shield of Missile Snaring being used to bash an opponent?

Answer 1

Improvised attacks with a magic item will overcome resistance

As of a 2018 errata to the Monster Manual, and books from the 10th printing on, monster vulnerabilities/resistances were changed from using "nonmagical weapons" to "nonmagical attacks". The section on "Vulnerabilities, Resistances, and Immunities" was also changed to read (MM page 8, emphasis mine):

Some creatures have vulnerability, resistance, or immunity to certain types of damage. Particular creatures are even resistant or immune to damage from nonmagical attacks (a magical attack is an attack delivered by a spell, a magic item, or another magical source). In addition, some creatures are immune to certain conditions.

The following description is given for improvised weapons:

Sometimes characters don’t have their weapons and have to attack with whatever is close at hand. An improvised weapon includes any object you can wield in one or two hands, such as broken glass, a table leg, a frying pan, a wagon wheel, or a dead goblin.

Often, an improvised weapon is similar to an actual weapon and can be treated as such. For example, a table leg is akin to a club. At the DM’s option, a character proficient with a weapon can use a similar object as if it were that weapon and use his or her proficiency bonus.

An object that bears no resemblance to a weapon deals 1d4 damage (the DM assigns a damage type appropriate to the object). If a character uses a ranged weapon to make a melee attack, or throws a melee weapon that does not have the thrown property, it also deals 1d4 damage. An improvised thrown weapon has a normal range of 20 feet and a long range of 60 feet.

From this description, a magic item can be used as an improvised weapon to make an attack as long as it can be held in one or two hands. As an attack delivered by a magic item, this fulfills the requirements to be considered a magical attack as described in the Monster Manual, and will overcome a monster's resistance to nonmagical attacks.

Answer 2

The Quick Answer: Check the item’s type and description

There are two ways to know if a magic item counts as a magic weapon:

1. It is a magic item of the type weapon
2. Its ability to attack as a magic item is specified in the description.

Magic Items of Type: Weapon

From Sage Advice Compendium 2016 reads:

Every magic weapon can bypass resistances and immunities to damage from nonmagical attacks, but only certain magic weapons are more accurate and damaging than their non- magical counterparts.

That is, the mechanic from some earlier editions, where a magic item needed a particular bonus to damage a creature, is gone. Now, you just have to confirm whether an item is a magic weapon.

The type appears immediately below the name of the magic item in the block. (See Magic Item Categories, DMG p. 139) Swords, bows, and other weapons appearing in the weapons table of the Player’s Handbook are typically magic weapons.

Usually, but not always, the weapon will also be specifically called out as “this magic sword” or “this magic weapon.” (Oathbow is an example where the magic weapon is referred to simply as “this weapon.”)

Other Items that can be wielded as magic weapons

If the item's description specifies so, the item can be used to attack as a magic item. For example, the Staff of Power (DMG, page 203) can.

This staff can be wielded as a magic quarterstaff...

Jeremy Crawford: Improvised magic items are not magic weapons

Jeremy Crawford tweeted about magic items used as magic weapons back in 2013, clarifying that when used as improvised weapons, they do not count as magic weapons.

Crawford stated:

A +1 shield gives a bonus to AC. The bonus has no effect on an improvised attack roll you make with the shield.

And then, when asked:

Would [a shield +1] still count as Magical for Resistance/Immunity to non-magical B/P/S attacks

Crawford replied:

A magic shield is not a magic weapon, unless its text says otherwise.

Reference

Some Weapons with Magic Effects upon them are NOT magic weapons

In your example of a sword that has a magical effect, this may or may not be a magic weapon. If the item is from published Wizard's material, check the above criteria.

If it’s an custom item invented by your DM then you just need to ask (or if you are the DM, just decide). It would be fine to have “wondrous item” that happens to be a weapon. For example, a non-magic axe might have a magic handle (fashioned from wood of the rubber tree plant) that allows it to be changed into a hand axe, battle axe, or halberd.

Magic Items as Improvised Weapons

A magic item that is used as an improvised weapon, such as a wand being used as a club, functions no differently than any other improvised weapon as far as dealing damage. They are magic items but not magic weapons.

An item's Magic Item Resilience (DMG, p.141) may make an otherwise-delicate item usable as an improvised weapon.

(Regarding the specific example of Gauntlets of Ogre Power, I have to say, worn gauntlets don't feel like an improvised weapon to me, and I would use the unarmed attack rules, maybe making ruling to give a +1 to damage if I felt generous. Wearing gloves is not very improvisational. Gauntlets that are taken off and used to slap might be.)

Spells on Weapons

One final note, there are spells that can be cast on weapons that do not turn them into magic weapons for damage immunity considerations. Continual Flame (PH, p. 227) is an example.

If a spell makes a weapon a magic weapon, it says so. See Magic Weapon, PH p. 257.

Answer 3

Only magical weapons bypass immunities. Any other item—mundane or magical—does not qualify. Even if it's a magical shield or magical gauntlets. Even if they are being used as improvised weapons, they are still not classified as weapons; thus do not bypass the immunities. The exception to this is when the item specifically states it can be used as weapon; for example: Demon Armor allows the users unarmed strikes to be calculated with a +1 to attack and damage rolls, count as magical, and has a damage die of 1d8.

Answer 4

Attacks made with Magic Items are Magical Attacks

According to the Basic Rules:

a magical attack is an attack delivered by [...] a magic item

There is no requirement for the item to be a "melee weapon", a "magical weapon", or even a "weapon" at all.

• A Shield of Missile Snaring is a magic item.
• Bashing a werewolf over the head with a Shield of Missile Snaring is an attack delivered by a magic item, and so it is a magical attack.
• Since it is a magical attack, it bypasses the werewolf's immunity to nonmagical physical damage.