Can I cast Darkness in my mouth so I can turn it on/off each round without having to use an action?

Question

I am playing a 5e game, and I had the idea of casting darkness in my mouth, or on a small rock that I then place in my mouth.

At the start of each of my turns, I close my mouth. This obscures the darkness, giving my character full visual sight during their turn. Then, at the end of my turn, I open my mouth, obscuring the character in complete darkness.

This presumes a character could open and close their mouth as free actions during their turn. And since they can speak freely, under normal circumstances, I don't see why this wouldn't be allowed. Other than it feels spell-breaking, in that it becomes OP in a way probably unintended.

The idea of casting the spell on the rock is so that you could also spit the rock out on the ground and keep moving. Or spit the rock into your hand and throw it in a cardinal direction.

I think it would also be fun if during this time when my mouth is closed to obscure the darkness, I'm not able to speak more than a mumble IRL to the other players.

I'm going to bring this up with my DM before attempting it, but I wanted to get some thoughts on the concept first.

Is this possible within the rules? Am I missing anything obvious?

Answer 1

This Would Not Work

...but not because of the way the Darkness spell works.

This wouldn't work because of an issue with the way combat happens. Combat is taken in turns, but it doesn't actually happen in turns. Mechanically, only because of how hard it is to actually do otherwise, combat is consecutive, but in actuality, combat is simultaneous.

Everyone is supposed to be fighting and defending at the same time, just your reaction times are different. Which means that open and closing your mouth during your turn won't actually do anything, since everyone else is attacking and defending during the same period of time as well. All that would happen is that there would be a strobe effect in the middle of you trying to kill each other.

Answer 2

Inside your mouth is not a legal target

Only points in space or objects are legal targets for darkness — since the inside of your mouth is part of you (a creature), you can’t cast it there.

Your PC’s mouth is also likely not opaque

You could fix the targeting by casting it on a marble or similar that you could place in your mouth after the casting, but then you have the problem that your mouth is unlikely to count as “opaque” by any of its senses (except the irrelevant one that describes an object’s shininess):

opaque, adjective

1. not transparent or translucent; impenetrable to light; not allowing light to pass through.
2. not transmitting radiation, sound, heat, etc.
3. not shining or bright; dark; dull.

The combined skin and lining of the human mouth is translucent, in that it permits light (but not distinct images) to pass through. Elven, gnomish, and etc. mouths are not known to be different from human mouths in this regard either.

As a way to get a “free” (and therefore infinitely-usable per turn) toggle control on darkness, it’s highly questionable.

A dragonborn's scales might make their mouth opaque — check with your DM about this, but mind that contrary to appearances, scales are often translucent like skin, too. Even then, also mind that you'll likely still have to use the action economy as below, anyway.

How to toggle darkness for cheap, but not free

You have one item interaction per turn that won’t cost an action. Any scheme for toggling darkness will use that, even if it's in a somehow-opaque mouth, because of the aforementioned game-breakage.

So, to toggle darkness in a way that any PC race can use and keeps the game intact, just secure your marble to the inside of a small light-tight box tied to your belt; use your free item interaction to flip it open or closed.

That’s as big as this exploit really gets, and it’s not that powerful.

Answer 3

This would violate the Object Interaction Rules

In 5th Edition D&D, you're granted 1 free object interaction per turn, limited to only simple interactions. Opening your mouth probably counts (to make the object visible) and closing it probably also counts (to make it obscured) but doing both in the same turn would require you to use the Use an Object Action.

It might seem strange, but mechanically, it's not requiring (substantially) more effort than lifting said rock out of your pocket + putting it back.

A Thief archetype Rogue might have an easier time of it

Thief Archetype Rogues gain the Fast Hands feature at level 3, permitting them to perform the Use an Object Action as a Bonus Action instead. So theoretically, as a Thief Rogue (multiclassed with whatever class gives you Spellcasting abilities), you could

• Close your mouth (Free Object Interaction)
• Cast a Spell or make an Attack (Action)
• Open your mouth (Bonus Action)

You could also do something less disgusting, like putting the rock inside a latched box that you then open + close using this sequence.

Some DMs are particular about the Simultaneity of Combat

Because the separation of combat into distinct "turns" is meant to be an abstraction of real-time combat, some DMs interpret this as meaning that it's not possible to meaningfully "strobe" an effect like this without some delayed interaction (i.e. a Reaction used on someone else's turn). The degree to which this is RAW is hotly contested, but this is a common interpretation of the rules.

So as a result, some DMs may rule that this is what actually happens:

• You close your mouth (Free Object Interaction)
  • The Darkness effect may or may not vanish, depending on what happens before your turn ends
• You make an attack or cast a spell. If you open your mouth later in this turn, the attack is made with Disadvantage, or the spell must not require visibility of the target
• If you open your mouth the Darkness effect doesn't vanish.
• If you instead choose not to open your mouth, the Darkness effect does vanish (becomes obscured by your mouth) at the time you close your mouth (???)

Again: I am not certain that is a RAW ruling. I'm just informing you that that is a ruling many DMs make.

Human[oid] biology is disgusting

Strictly RAW, the Darkness effect spreads around corners, and so long as there is an unbroken path to all points within its radius, the Darkness spreads to that point. So some DMs may rule that the inside of your mouth (which is connected to your nostrils, even your ears to a degree, through your windpipe...) does not adequately obscure the Darkness effect. This may vary depending on the creature's race, but 5e doesn't describe in precise detail how the anatomy of other Humanoid races vary from the anatomy of humans.

Answer 4

While opening and closing your mouth might be free, timing it such that you don't hinder your allies and blind your enemies in the exact moment they take aim looks complicated enough that you should not be able to do it freely. Also, this may not prevent the enemies from delaying the attack until you close the mouth again, effectively having them attack first as soon as vision is restored (thus not having any practical effect in the attack sequence)

Answer 5

I don't think it would work, at least for most races. Per the Darkness spell:

Completely covering the source of the darkness with an opaque object, such as a bowl or a helm, blocks the darkness.

Oral cavities are not opaque (try putting a flashlight in your mouth), and I'd extend that to all normal player races. I could see this working with, say, a stone golem.