D&D 5E How does Mage Slayer feat reaction attack sequence with the spell effects of the triggering caster?


So if I have the Mage slayer feat and 5 feet away from a caster and he casts a spell, does my reaction attack come before, simultaneous with or after the spell effects?

My initial intuition is the reaction attack occurs simultaneously with the casting and prior to the effect, similar to counterspell which has the same trigger and happens before the spells effect takes place.

Example situations:

1. If he casts misty step do I get to attack him as he teleports away

2. If he casts hold person on me do I have to save against being paralyzed before I attack him or do I attack him and then save and if I attack him and hit him does he have to make a concentration check even though the spell is not in effect yet?

3. If he casts green-flame blade on me and my reaction attack kills him does he still get to roll his attack and damage?
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5e appears to have avoided the 4e clarification of having "interrupts" and "reactions", so we are left with no rulings of any of this that I can see.
Personally I just look at the intent of the power, some reactions would be worthless if they did not work in a certain way. I think that the vast majority of the time I would say the attack is resolved before the spell, even though the spell triggers it. So the mage gets attacked before Misty Step goes off etc.


Mod Squad
Staff member
The DMG says,

"Typical combatants rely on the opportunity attack and the Ready action for most of their reactions in a fight. Various spells and features give a creature more reaction options, and sometimes the timing of a reaction can be difficult to adjudicate. Use this rule of thumb: follow whatever timing is specified in the reaction’s description. For example, the opportunity attack and the shield spell are clear about the fact that they can interrupt their triggers. If a reaction has no timing specified, or the timing is unclear, the reaction occurs after its trigger finishes, as in the Ready action."


The specific wording of the feat is:
  • 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.
Which implies the spell is actually cast (and completed). It doesn't say "attempts to cast..." or "starts to cast..."

Contrast this to counterspell's wording "You attempt to interrupt a creature in the process of casting a spell..."

So I think. with this feat, the intent is to hit a creature that has already cast a spell - not to interrupt it.


Scion of Murgen (He/Him)
RAW states a reaction can come before or after. PHB pg. 193.

PHB pg. 193 states no such thing. There's no general rule for reaction timing in the PHB, each specific reaction has its specific timinig.

Pg. 193.
"When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger."
Page 193 says it's after, or you skip your chance.

Xanathar's and the DMG say it's after, unless the effect specifies otherwise.

Which is definitely a bummer for Mage Slayer, since it doesn't specify. I may house rule that.

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