D&D 5E Opinions on a couple of situations, please!

[Sebastrd]

1. PC invisible (via dust of disappearance). Moves hex spell to a new target. Lose invisibility?

No. Invisibility specifically states, "The spell ends for a target that attacks or casts a spell." You're doing neither here.

2. Bonus action spell already cast. Activate magic item to cast fog cloud (magical bard instrument). Violates bonus action spell/only one action cantrips rule?

It depends on how you interpret the rule for using an item. Personally, I think magic items should be special. Technically, since you're using an action to play an instrument that happens to cast a spell, I'd allow it. However, another DM might rule otherwise given that the item description does say, "You can use an action to play instrument and cast one of its spells."

 

[ExploderWizard]

Breath weapons do not require attack rolls nor are they spells so we are supposed to believe that the 15 soldiers who were just reduced to bits of ash were not attacked?

I prefer to use the common English meaning of attack and instead permit the casting of spells while invisible as long as they are non-hostile. In any event keyword shenanigans that produce results such as the breath weapon example given are a good reason why such constructs are of little use.

 

[Arial Black]

I agree, Arial Black, that , technically, Hex is not an "attack", nor are you "casting a spell" by shifting an existing Hex. It would seem that this is a loophole for invisibility.

By that definition, PCs with ongoing effects (that have already been cast) can be turned invisible, then continue to: Call Lightning down upon foes, Flaming Sphere them, Moonbeam groups of unfortunates.

None are "attacks", as such, and the spell has already been cast. Go the invisible druids!

Yep, things work how they say they work. Creatures will soon learn to take advantage of the way things actually work and do things like use Dust of Disappearance so they don't have to use up their concentration maintaining invisibility, and use magic items that work without allowing you to 'cast a spell'.

Creatures will base strategies around 'how things actually work', and not around 'how we think things aught to work'. Evolution in progress.

It's wrong for the DM to change the way things actually work on a whim during the action just because the DM thinks it should work another way, while claiming his made-up rubbish is actually the rules. Imagine playing a game of chess when out of the blue your opponent claims that queens can jump over pieces just like knights; his house his rules.

The DM might wish that invisibility is lost for anything that the DM wants to interpret as hostile, but it doesn't. 'Attack' really does have a specific rules meaning in 5E, and to pretend on the fly that it doesn't means that the DM is failing in his duty to conduct a fair game.

If the DM wants to create a houserule about what negates invisibility then he should state it up front before character creation. If that's the way his world works then PCs should be made knowing that. It shouldn't be a 'gotcha' to a PC made under the assumption that the invisibility rules are as written.

 

[Arial Black]

Breath weapons do not require attack rolls nor are they spells so we are supposed to believe that the 15 soldiers who were just reduced to bits of ash were not attacked?

I prefer to use the common English meaning of attack and instead permit the casting of spells while invisible as long as they are non-hostile. In any event keyword shenanigans that produce results such as the breath weapon example given are a good reason why such constructs are of little use.

Yeah, I prefer to use alternative common English meanings of rules wordings too. In my games minor illusion can only create images of children who are not legally adults.

What? It's a 'common English meaning' of the word 'minor'! What's the problem?

Or could it be that 'rules' use certain words in a certain way?

 

[Satyrn]

Yep, things work how they say they work.

But what's interesting to me is the first half of the rule you've been referencing. The part that says "if there's a question." I read that to mean I don't have to consider the second part if I'm already decided that a dragon's breathing on the PCs is an attack (it really really should be!) or if transfering a hex is, too.

Now if I really start waffling on whether I ought to rule it's an attack, then I'd say "yeah, I'm questioning this, so I'll consult with what the second bit says now, and go with that."

That is how I deal with it.

 

[jaelis]

I'm sympathetic to someone who wants to play that any hostile action ends invisibility. Not so sympathetic to wanting to redefine what an attack is to achieve that. Lots of rules key off attacks, should they all work with dragon breath etc?

 

[Satyrn]

I'm sympathetic to someone who wants to play that any hostile action ends invisibility. Not so sympathetic to wanting to redefine what an attack is to achieve that. Lots of rules key off attacks, should they all work with dragon breath etc?

If it makes sense that it would, yes.

But you'd have to show me these lots of rules, because I'm not sure they exist the way you're suggesting they do. That is, I'm under the impression that most of of them that really shouldn't work with dragon breath refer to a "weapon attack," which nicely covers that problem for me.

 

[jaelis]

Well, here's a few:
Uncanny dodge, Soul of vengeance (paladin), ending a barbarian's rage, Sentinel feat, adjudicating total cover, popping mirror images, triggering sanctuary, ending calm emotions, triggering shield...

 

[Satyrn]

I looked up a couple of those (uncanny dodge, sentinel) - plus from what I remember about sanctuary, or ending rage - I'm thinking you're convincing me that my method will work just fine.

They all seem like they ought to apply to a dragon breathing fire.

Although I will admit it looks like Uncanny Dodge looks like it wasn't meant to apply there, what with Evasion coming on line a couple levels later for the rogue. Although I will justify that by considering Evasion to be an improved (under certain conditions) Uncanny Dodge . . . even though it's still wonky that taking half damage from evasion would maybe still let the rogue use his reaction to Uncannily Dodge that, quartering the damage.

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Oh, sanctuary. That feels like a better illustration than the OP's invisibility for this question. While I might question if moving hex onto a creature ends invisibility, I would rule in a heartbeat that you couldn't just move it onto someone affected by sanctuary.

 

[jaelis]

So popping mirror image with an AoE is cool? And total cover blocks all AoEs? Barbarian activating a magic item can keep his range going?

To me, if you're going to rule this way it just makes a lot more sense to take things case by case. The quarter damage thing with UD certainly doesn't seem intended to me and it makes UD quite a bit more powerful.