D&D 5E Magic Mouth visual trigger & invisibility

[Zinnger]

Magic Mouth can be set to trigger based on "visual or audible conditions". So what happens if you set it to trigger on a creature passing within 30 feet but the creature is invisible? What if it is a rogue and the stealth check beats the spell DC of the caster? Does the mouth still speak or must the intruder be "visual" to the spell? Thanks for any ideas on how to handle this.

 

[iserith]

Magic Mouth can be set to trigger based on "visual or audible conditions". So what happens if you set it to trigger on a creature passing within 30 feet but the creature is invisible? What if it is a rogue and the stealth check beats the spell DC of the caster? Does the mouth still speak or must the intruder be "visual" to the spell? Thanks for any ideas on how to handle this.

From the spell: "The triggering circumstance can be as general or as detailed as you like, though it must be based on visual or audible conditions that occur within 30 feet of the object. For example, you could instruct the mouth to speak when any creature moves within 30 feet of the object or when a silver bell rings within 30 feet of it."

It would very much depend on the "triggering circumstance," but I'd rule that in general invisibility would not meet the requirements of a trigger that is based on visual conditions. The same goes for a stealthiness and a trigger based on audible conditions. It seems like in some cases, the trigger can be based on both conditions.

If you're a player using this spell and not the DM, I'd make your intent clear to the DM in this regard as well.

 

[Mercule]

I would rule that the Magic Mouth cannot act as an Alarm spell for invisible foes, out of the box.

 

[jgsugden]

If the PC doesn't specify an audio trigger, I generally assume they mean a visual trigger. So, if they say there must be a creature nearby, I assume there is a visible creature nearby (within 30').

If a player specified the trigger as hearing a creature, I'll generally assume it can be defeated with a stealth check (default DC 15).

If a player specified see or hear a creature, invisibility would defeat the see and a stealth check of 15 would defeat the hear...

 

[I'm A Banana]

Magic Mouth can be set to trigger based on "visual or audible conditions". So what happens if you set it to trigger on a creature passing within 30 feet but the creature is invisible? What if it is a rogue and the stealth check beats the spell DC of the caster? Does the mouth still speak or must the intruder be "visual" to the spell? Thanks for any ideas on how to handle this.

Invisible creatures aren't soundless, so presuming the conditions aren't entirely visual, I think it'd still go off. A stealth check by an invisible (or otherwise unseen) character would be the way I'd handle someone wanting to not trigger it audibly OR visually.

 

[miniaturehoarder]

What if it is a rogue and the stealth check beats the spell DC of the caster?

I'd treat the magic mouth as 'seeing' anyone that can be seen, IE not invisible, not behind total cover.

 

[Rocksome]

I'd also consider allowing the use of a See Invis spell at the time of casting Magic Mouth to allow it to sense invisible creatures.

 

[sy28]

Even if someone was invisible, them moving would make SOME noise no matter what. If you are corporeal in some way then you move air around when you move. That would make noise. That noise would be extraordinarily slight, to the point that no normal living thing could hear it. However, Magic Mouth isn't a normal living thing. It's MAGIC. It absolutely could be used to detect an invisible creature.

If a PC had the trigger something like, "say 'Warning' when a hostile invisible creature makes any noise within the range of the object" that would totally work. That's RAW. If you wanted to houserule against that you could, but you'd be wrong to say that the spell didn't work that way. You need to remember this is only 30 feet. It's not a huge range. Invisible creatures could still attack from range without having any PCs being warned.

 

[5ekyu]

Even if someone was invisible, them moving would make SOME noise no matter what. If you are corporeal in some way then you move air around when you move. That would make noise. That noise would be extraordinarily slight, to the point that no normal living thing could hear it. However, Magic Mouth isn't a normal living thing. It's MAGIC. It absolutely could be used to detect an invisible creature.

If a PC had the trigger something like, "say 'Warning' when a hostile invisible creature makes any noise within the range of the object" that would totally work. That's RAW. If you wanted to houserule against that you could, but you'd be wrong to say that the spell didn't work that way. You need to remember this is only 30 feet. It's not a huge range. Invisible creatures could still attack from range without having any PCs being warned.

"Visible or audible conditions" PHB

And so...

"If a PC had the trigger something like, "say 'Warning' when a hostile invisible creature makes any noise within the range of the object" that would totally work. That's RAW."

Really? RAW? Deciding against that condition is house rules?ok, so I will bite, what is the RAW visible or audible conditions thst indicates a creature is hostile as opposed to totally any other creature making noise?

 

[Mort]

If a PC had the trigger something like, "say 'Warning' when a hostile invisible creature makes any noise within the range of the object" that would totally work. That's RAW. If you wanted to houserule against that you could, but you'd be wrong to say that the spell didn't work that way. You need to remember this is only 30 feet. It's not a huge range. Invisible creatures could still attack from range without having any PCs being warned.

Noise, sure, the magic mouth could trigger on that.

But hostility? Intent isn't part of the spell.

If the magic mouth could discern intent, it would jump from niche use to one of the most potent spells in the game!