D&D 5E Invisibility, non-instantaneous spells, and spell effects

[Irlo]

Disclaimer: What follows, sparked by the comment quoted below from another thread, is meant to be a good-natured digression and exploration of spell mechanics and is not intended to challenge anyone's interpretation of RAW. It's ridiculously pedantic and should be taken in that spirit.

EDIT: I'm a DM. I know what my ruling would be. This is a theoretical discussion about how folks on the forum interpret spell mechanics. Thanks!

Things that are instantaneous are labeled as such.

The spell invisibility is not instantaneous in duration, nor are the spell effects specified to be instant. Can I cast a readied magic missile to use when the target begins to turn invisible? Why or why not?

YES. It takes only a fraction of a second to use a spell as a reaction. The invisibility spell does not specifically state that the invisible condition is applied instantly, so there is some small but perceptible duration of time after completion of spell that the target is visible and fading away. Plus, I like the idea of a quick but gradual fade-away as the magic kicks in.

NO. The magic missile spell is only valid on a target that the caster can see. Spell effects occur instantly upon competion of the spell unless stated otherwise, and don't require an instantaneous label or descriptor to be instantaneous. [Is there a rule to that effect, or is it just a reasonable ruling on the part of the DM?]

 

[payn]

I just use initiative for this.

 

[Irlo]

I just use initiative for this.

I'm assuming combat has already begun and a caster has used the ready action to prepare magic missile.

 

[Hand of Evil]

What does your GM say, they have the final say no matter what is debated here? It is based on the Initiative.

Now, you have every situation to think about.

 

[payn]

I'm assuming combat has already begun and a caster has used the ready action to prepare magic missile.

In that case, I dont typically allow this level of granularity of ready action. They either blast them with missile before, or the target goes invisible, they dont happen simultaneously.

 

[Cruentus]

I would have the player who is readying identify when they will cast magic missile:

1) When an enemy begins to cast a spell? (Any enemy, the first enemy?) - ok.
2) When an enemy goes invisible? For me, that's not a sufficient trigger. What happens if they Misty Step? It looks like invisibility when they vanish, for example.

The player also wouldn't be able to know if the enemy was casting Invisibility anyway, so that wouldn't be a trigger either, at least in my interpretation.

 

[TaranTheWanderer]

I’d allow you to hit them as they cast. As they dance their jig and as they are verbalizing those invisibility adjectives. And, finally, the moment you see that gum arabic, you’re like, “THIS IS IT!”

You let those missiles fly. He completes the spell and turns invisible but it’s too late because those darts of force are already en route, homing in on the intended target. Make a concentration check, bub.

 

[James Gasik]

The Ready rules say you can respond to a particular, perceivable circumstance. But that the action goes off after the trigger. If the trigger is "the enemy becomes invisible", it comes down to the DM's interpretation of whether you vanish all at once or fade from view gradually.

I think most tables would run it as an instant "Ninja vanish!" and thus you can't react to the trigger, because after the trigger has resolved, magic missile no longer has a legal target.

If, however, you readied against casting a spell, that certainly works because you have to complete the components of the spellcasting- even if they don't require a lot of fanfare, it takes at least some time to shake your arcane focus and shout "Evanesco" (or whatever the kids are saying these days).

 

[Dausuul]

My ruling would be no. A readied action happens immediately after the triggering event unless otherwise stated; you can't get around that by saying "I ready for when [triggering event] begins to happen."

In general, I'd say by the time you see your opponent start an action, you've lost your chance to pre-empt it with a readied response. Once they start, you can't respond till they finish.

The exception would be if the action has discrete pieces such that the person acting can do other things (e.g., move) in between. So you could ready for an enemy's attack, and you'd go after their first attack but before the second. But you can't ready for when they "start to attack"--they always get the first swing.

 

[James Gasik]

The ready rules don't say anything about responding to actions, just responding to triggers, "a particular, perceivable circumstance". Could I not ready to act when an archer draws back their bow, and then have my readied action trigger before they loose the arrow?