Making a Shield of Expression detect invisibility with Magic Mouth

[Reynaerde]

Hi there everybody, I'm coming to you with a somewhat weird project that I could use some suggestions for!

As you could already guess from the the title, the whole thing is about finding some creative ways to make use of a common item and an often ignored spell. The item in question is a Shield of Expression from Xanathar's Guide to everything (use a bonus action to change the expression of the face on the shield) and the spell is Magic Mouth, which as some of you might know has some interesting characteristics like perfect vision and hearing, incredibly detailed triggers, being able to be triggered multiple times without losing its magic, and maybe most importantly: making the words appear to come from the object's mouth if it has any (which the shield obviously does).

Since this is basically an in-character project for a Whisper Bard with intelligence 12 (check this mini-guide to get an impression of what kind of build I went for), I'm not planning to unleash a technological revolution here. That being said, I could use some additional inspiration for other cool things I might be able to incorporate in my design:

Muttering Shield of Expression

• Whisper “Prowler” whenever a creature within range and facing the shield makes a sound but is not visible
• Whisper “Skulker” whenever a creature within range and behind the shield makes a sound but is not visible
• Happily call out “Quincy” whenever someone in a white mask with a black jester cap enters range (this is a description of our mysterious adversary, and the name is the name of her suspected real identity)
• Slowly start chanting an ancient curse whenever the shield gets hit
• When the face changes to happy : manic chuckle
• When the face changes to sad : sorrowful moan
• When the face changes to angry : muttered string of curses
• When the face changes to scared : suppressed scream
• When the face changes to surprised : “what the ****?!”
• When the face changes to contempt : exasperated “tsk tsk”
• When the face changes to disgust : feigned gagging sound

What kind of triggers do you think I could add? I'm just as happy with flavorful or fun ones as I'm with triggers that could be actually useful in terms of exploration/detection. Do you think my list of expressions has enough options? I pulled these from some list of (apparently) universal facial expressions, but I might be missing some obvious ones.

All suggestions are welcome!

[XmonkTad]

Trapfinding is my next thought. Since we're using magic mouths divination capacity, finding traps and pitfalls and "structural weaknesses that dont count as traps but will still hurt you if you walk on this" would be useful.

[KorvinStarmast]

Brilliant. My son's barbarian has one of those shields. I wonder if the party sorcerer would be interested in this trick. *golf clap*

[Talsin]

...

• Whisper “Prowler” whenever a creature within range and facing the shield makes a sound but is not visible
• Whisper “Skulker” whenever a creature within range and behind the shield makes a sound but is not visible

...

While I like the arcane programmer fun, I'm not sure if direction is something the spell may be able to handle. You can include the shield in the detection since it technically wouldn't be part of the spell.
Also, remember that it's only a 30ft radius, so it won't be perfect detection.
Additionally, you may want to have a neutral face, or something that is a negative control for all of these, as in "If condition X, AND the face is NOT neutral, say Y". That way you can stealth/silence your shield.
I also suggest that whenever you defeat specific monster types that it have certain catch phrases!

• Plant-type? "Timber!" or some kind of reference to Topiary...
• Vampire? "Another one bites the dust!" or "All we are is dust in the wind" if you want to separate facial features for it since that can be another layer.
• Zombie? "Aaaaand Stay Down!"
• Wereshark? "That was Jawsome!" ...wait a minute...
• Sees the Tarrasque (or any creature of a similar size)? "Oh, it's waaaaaaaay bigger up close!"

I think you get the idea...

[Talsin]

Someone other than you takes the shield "Help, I'm being stolen!"

[Chronos]

Of course, most of this is just Magic Mouth, and could be used on any item. It being a Shield of Expression makes very little difference.

[Reynaerde]

Trapfinding is my next thought. Since we're using magic mouths divination capacity, finding traps and pitfalls and "structural weaknesses that dont count as traps but will still hurt you if you walk on this" would be useful.

That's an interesting idea, how would you phrase the trigger for that?

Brilliant. My son's barbarian has one of those shields. I wonder if the party sorcerer would be interested in this trick. *golf clap*

If scrolls are available in your campaign the barbarian could buy the Magic Moth scroll(s) himself, making sure it doesn't cost the sorcerer anything.

While I like the arcane programmer fun, I'm not sure if direction is something the spell may be able to handle.

I'm also not quite sure yet if I want to burden the DM with that extra bit of bookkeeping.

Also, remember that it's only a 30ft radius, so it won't be perfect detection.

Yeah, it's more of a last minute "oh crap" kind of thing.

Additionally, you may want to have a neutral face, or something that is a negative control for all of these, as in "If condition X, AND the face is NOT neutral, say Y". That way you can stealth/silence your shield.

That is an excellent point!

I also suggest that whenever you defeat specific monster types that it have certain catch phrases!

Those are hilarious and awesome!

Someone other than you takes the shield "Help, I'm being stolen!"

Great idea!

Of course, most of this is just Magic Mouth, and could be used on any item. It being a Shield of Expression makes very little difference.

Of course! What the shield of expression adds is "just" a flavorful visual element that brings some personality to these magic mouth triggers. Funny enough, though, it feels quite a bit more magical to me than the majority of items in the DMG.