As a departure gift to a member of our party, I wanted to give a pendant with Magic Mouth on it, the trigger condition being "when a creature that you're having a conversation with lies to you". The DM argued that the spell gives the object the ability to "see and hear", but cannot make rolls, and as such, it cannot know when a creature is lying. Which I'm cool with, since he is the DM.
I'm DMing an upcoming Ravnica campaign and a player expressed their interest in using Magic Mouth sorta like Programming which I know nothing about but it seems both creative and fun enough for me to allow. Thing is, the lie detector thingy bought up a bunch of questions in my head about how much "sensitivity" or "objective knowledge" about the world the Magic Mouth could actually work with, and I would like a frame of reference for the upcoming Magic Mouth shenanigans.
- The Magic Mouth spell never states that it's providing the object with "the ability to see and hear", just that it triggers when a thing happens and such trigger must be based on visual/audible conditions. The spell does not specify whether those perceptible conditions are or are not relative to the caster's senses. How much abstraction would you feel is correct to get away with when casting the spell? If in darkness, would a "when a creature approaches" condition would still trigger, even if it's not technically possible to see for a caster who lacks darkvision? If it does so, what about conditions increasingly more specific such as "when a creature breathes" / "when a heart beats" / "when the spectrum of color is reflected on a surface" (which is pretty much always). The fact that humanoid creatures have certain limitations in regards of how their senses interact with the world doesn't seem to implicitly impose a limitation on the spell, and since, for example, atoms always posses energy, you can technically always have a "visual condition" to be triggered, when would you put a limit to this arbitrarily high perception?
- The spell allows for conditions as general or complex as the caster wants. How would you go about, for example, the "lie detector pendant" thingy in regards to how much "objective knowledge" the mouth can obtain, since while the spell does not implicitly provide the mouth with these skills, it also does not disregard them.
I dunno, maybe kinda overreacting here since it's my first time DMing and you know how that goes.