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

[James Gasik]

That doesn't mean there aren't reasons for attempting this sort of thing, however. The enemy could die. Or your attack could have a rider that will prevent them from fleeing, like knocking them prone, pushing them over a cliff, what have you.

 

[Flamestrike]

Can I cast a readied magic missile to use when the target begins to turn invisible? Why or why not?

A readied spell is cast as a reaction.

Xanathar's Guide to Everything outlines the general rule for the timing of reactions:

If you’re unsure when a reaction occurs in relation to its trigger, here’s the rule: the reaction happens after its trigger completes, unless the description of the reaction explicitly says otherwise.

Magic missile states:

You create three glowing darts of magical force. Each dart hits a creature of your choice that you can see within range.

1) Spell gets cast,
2) the target is now invisible,
3) you now take your reaction,
4) you cant see them, so
5) you cant target them.

I'd rule you cant target them.

That said, it does depend on the trigger you stated for your readied action. Notably the trigger does not have to be an action, just any 'perceivable circumstance':

Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn, which lets you act using your reaction before the start of your next turn.

First, you decide what perceivable circumstance will trigger your reaction.

A trigger of 'if the Caster opens his mouth' I cast, might be sufficient to get the spell away before the spell is completed.

 

[Lyxen]

A few points:

• As proven in another thread, instantaneous does not mean "zero time", since things can be sequenced (multiple examples given)
• I'm very fond of this, because in the genre, nothing is ever really instantaneous, otherwise it would not be really perceivable, and therefore not look cool.
• Which is why, with the openness of 5e, I like to describe by effects probably in slower motion than most DMs (again, it's not mandatory, it's just that 5e clearly allows it).
• So just as teleport would have a fade in / fade out, invisibility would have a fade out, because it looks way cooler.
• And this despite the fact that the spell indeed does not have an instantaneous duration, I completely agree that this is not particularly RAW.

So I would allow it. Again, if someone can predict that an opponent will turn invisible and is ready to bet his action on it, he should be rewarded if it turns out to be the case.

 

[Plaguescarred]

Taken that you select a spell's target(s) when you take your readied action and release the spell, which take place after the triggering spellcasting occur, any readied spell targeting creature you can see will only be able to target those you can see at this moment. If the caster is now invisible, it won't be a valid target for Magic Missile.

There is a Sage Advice on this question Rules Answers: June 2016 | Dungeons & Dragons

For readying a spell or other action, does the target have to be in range? Your target must be within range when you take a readied action, not when you first ready it.

 

[jgsugden]

How would I handle it? I'd put aside RAW and dig in with the player. This is a chance to do something with a little anticipation involved, which is always good.

Player: "I want to ready my magic missile spell to nail him if he turns invisible. Can I do that?"

DM: "Stop picking your nose. That type of split second timining would be difficult. It might not work. Are you waiting for him to start to fade out of existence, or are you looking for something else?"

Player: "Hmmm... I don't actually know that he cast a spell to turn invisible earlier, do I? Hmmmmm... I guess I have to wait to start to see him disappear."

DM: "Did you just eat .... never mind. I don't want to know. OK, you're going to focus on the second when he starts to disappear. You'll need to wrap up your spell in a very tight window. You'll have to make a tough arcana check for it to work - if he even turns invisible. He might not.
Is that what you want?"

Player: "Yes. I've got a pretty good arcana skill."

DM:" Well, he goes next, and he does cast an invisibility spell as he prepares to escape."

Player: "Shoot - this would have been easier if I'd triggered off spellcasting rather than them disappearing, right?"

DM: "Much. Regardless, as he disappears you wrap up your spell and release the magic. Roll Arcana. The DC is 18."

Player: ".... 17."

DM: "You release the spell and the magic missiles fly from your hand in his direction, but as he disappears they lose their lock on him and fizzle out, striking nothing."

 

[Oofta]

I rule that you can ready to cast when someone starts to cast, whether or not it's obvious the target is casting a specific spell is a different issue. Same way you can tell that an archer is about to fire an arrow because they knock an arrow and pull back.

However, in general you would not know the spell being cast quickly enough to complete the readied action before the target became invisible.

 

[Flamestrike]

Player: "I want to ready my magic missile spell to nail him if he turns invisible. Can I do that?"

Seeing as your [perceivable circumstance trigger] is [him turning invisible] and you cant target an invisible creature with magic missile, the answer is no.

If your [perceivable circumstance trigger] was something other than 'when he turns invisible' we could talk.

 

[Lyxen]

Taken that you select a spell's target(s) when you take your readied action and release the spell, which take place after the triggering spellcasting occur, any readied spell targeting creature you can see will only be able to target those you can see at this moment. If the caster is now invisible, it won't be a valid target for Magic Missile.

I agree with the reasoning, although honestly, if I was casting MM, I would cast it when he starts casting, whatever he is casting, or I would prepare an AoE if he turned invisible, the combination of MM + Becomes invisible is strange to me.

 

[Umbran]

In this case, the casting of the magic missle was mostly completed on that player's turn and held, per the ready action rules

Okay, fair. I should have reread, rather than go from memory. Point taken.

But if you want to invoke those rules, you must first establish that "start to disappear" is an observable event - if the GM has not established invisibility as a slow fade, then you must establish this before it is a valid declaration for a Ready action. If it comes in at the blink of an eye, you're out of luck.

1) Be watching for the enemy to start to become invisible, regardless of the cause. (The trigger is "start to become invisible," although perhaps "start to disappear" might be better?)
2) Interrupt with the reaction to release the spell.

So, reading those same ready action rules, you don't "interrupt". Specifically, "When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger." You do not interrupt the trigger - the trigger completes.

When does "start to disappear" finish? When the target has completely disappeared! There is no other clearly defined "end of the start."

 

[TaranTheWanderer]

-I ready to cast magic missile when they cast a spell
-Your readied action goes off directly AFTER the triggering action occurs
-They cast Alarm...as a ritual
-10 minutes later: you cast magic missile