D&D 5E Mage Slayer FEAT

[maritimo80]

The Wizard with this feat can use your reaction to make a melee weapon attack
against que creature that uses a Magic Item, as Necklace of Fireballs?


That is, a magic item of attack is considered spell cast for this talent?

Mage Slayer
You have practiced techniques useful in melee combat
against spellcasters, gaining the following benefits:
• When a creature within 5 feet of you casts a spell, you
can use your reaction to make a melee weapon attack
against that creature.
• When you damage a creature that is concentrating on
a spell, that creature has disadvantage on the saving
throw it makes to maintain its concentration.
• You have advantage on saving throws against spells
cast by creatures within 5 feet of you.

 

[Dausuul]

The Wizard with this feat can use your reaction to make a melee weapon attack
against que creature that uses a Magic Item, as Necklace of Fireballs?


That is, a magic item of attack is considered spell cast for this talent?

This is ultimately up to the DM, but I'd say that if the magic item explicitly says "You cast [X] spell," then that is considered casting a spell and would trigger Mage Slayer. An example would be the wand of magic missiles:

"While you hold this wand, you can use an action to expend 1 to 3 of its 7 charges to cast the magic missile spell without using any components."

If the item says it creates the effect of the spell, but doesn't use the word "cast," then Mage Slayer does not trigger. I don't have my DMG in front of me, so I'm not sure what the necklace of fireballs text says.

 

[Plaguescarred]

That is, a magic item of attack is considered spell cast for this talent?

I'd say no since you are not casting any spell but using a magic items that mimics the effect of one. While many magic items let you cast spells, the necklace of fireball let you throw beads that detonate as a fireball spell.

 

[Pauper]

The DMG specifies that you use an action to throw a bead, which would not be casting a spell for the purpose of the Mage Slayer feat.

It is also likely that using a scroll is not spellcasting for purposes of the Mage Slayer feat; the DMG notes that an action is required to 'read the scroll', which 'invokes' its magic. It does not state that the scroll user actually casts the spell inscribed on the scroll.

 

[Warmaster Horus]

I'd say it depends on whether the Magic Item you're using says you're casting a spell.

Staff of Fire
Staff, very rare (requires attunement by a druid, sorcerer, warlock, or wizard)
You have resistance to fire damage while you hold this staff. The staff has 10 charges. While holding it, you can use an action to expend 1 or more of its charges to cast one of the following spells from it, using your spell save DC: burning hands (1 charge), fireball (3 charges), or wall of fire (4 charges). The staff regains 1d6 + 4 expended charges daily at dawn. If you expend the last charge, roll a d20. On a 1, the staff blackens, crumbles into cinders, and is destroyed.

A Staff of Fire requires spell caster attunement and explicitly states you are casting a spell when using charges from it. Wand of Magic Missiles says that you cast the spell as well.

Wand of Magic Missiles
Wand, uncommon
While you hold this wand, you can use an action to expend 1 to 3 of its 7 charges to cast the magic missile spell without using any components. For 1 charge, you
cast the spell as if you used a 1st-level spell slot, and you increase the spell slot level by one for each additional charge you spend.

However a Potion of Gaseous Form, while casting a spell on you, is not a creature, so NO to Mage Slayer. Some other Potions don't even mention spell casting.

Potion of Gaseous Form
Potion, rare
This potion’s container seems to hold fog that moves and pours like water. When you drink this potion, it casts the gaseous form spell on you. The effect lasts for 1 hour or until you take a bonus action to end it.

So, I'd say check the item's description and if a creature is casting a spell, then YES, Mage Slayer applies.

 

[Wallraven]

Mage Slayer
You have practiced techniques useful in melee combat
against spellcasters, gaining the following benefits:
• When a creature within 5 feet of you casts a spell, you
can use your reaction to make a melee weapon attack
against that creature.

Would that happen during casting (possibly interrupting the spell), or after casting?

 

[Anth]

Would that happen during casting (possibly interrupting the spell), or after casting?

It doesn't say.
As it's a reaction I'd rule it works similar to an opportunity attack, possibly interrupting the spell. If you hit the caster has to succeed a concentration check not to lose the spell.

 

[transcendantviewer]

No, it does not trigger, because A). You are triggering an item, not using a Melee Weapon Attack; B). Technicaly making a Spell Attack; and C). You're making a Ranged Spell Attack to boot. Simplly put, the rules are clear on this: no spells as Attacks of Opportunity, unless you take War Caster, and even then, it has to be a targeted spell, not a Fireball, which is an AoE spell with a targeted point of origin. There's a difference. And no: magic items cannot be activated using this benefit, it explicitly states that it must be a spell.

 

[Sacrosanct]

The right answer is what makes most sense to your DM and players. Just make sure you agree before it comes up.