"You mumble asleep" vs "You mumble in your sleep"

“You mumble in your sleep” is correct. “You mumble asleep” is incorrect and does not make sense to a native speaker. Also, your question should be phrased as “are either of these incorrect?”

"You mumble in your sleep" is correct.

The second is correct. "Asleep" by itself cannot be used to mean "in your sleep".

You mumble in your sleep is better, though I’m not sure how to explain that.

You could say “ You mumble when you’re asleep”

Some examples of what you can say are: “You mumble while you are asleep.” “You mumble while you are sleeping.” “You mumble in your sleep.” Asleep is an adjective. Mumble is a verb. “You mumble asleep” does not work because you cannot describe a verb with an adjective. You would need to use an adverb to describe a verb. Example: “You eat quickly.” In the context of your question you might be tempted to use: “You mumble sleepily.” However, “sleepily” doesn’t really convey that the subject of the sentence is actually asleep. It implies the subject is awake but tired.

Just go with "you sleep mumble, dude". Works and it's got some flair. This is my favorite sub for all the unintentional comedy. It should be seen as the platonic ideal of pedantic nonsense. People ask what time it is an they get an explanation of how a watch works. It's people learning English and just wanting to sound at ease in the language but the responses act like they are helping defend a dissertation.

The first one is wrong. Asleep is an adjective so can't be used to describe mumble (a verb). You'd need an adverb for that. There isn't any adverb I'm aware of that means "while you're sleeping" so you would use an adverbial phrase like "while you're asleep" or "in your sleep" or something like that

You could repair "You mumble asleep." with 'while'. So: "You mumble while asleep." works ok.

"You mumble asleep." It doesn't make sense, but it sort of means that you mumble to fall asleep or something. I think if you wanted to tell someone that they mumble when they say the word "asleep," it can work

"asleep" as an adverb indicates that the verb **results** in sleep. it's not used to indicate that something happens in the middle of sleep.

There may be regional dialect variations, but I'd posit that the first one is incorrect, and without your second variation, I'd struggle to understand what you were meaning. "You mumble while you're asleep" would work.

You sleep mumble. This is not a great sentence, but it is more understandable to a native speaker. The second sentence is the best and most common parlance.

"You mumble in your sleep" is correct. "You mumble asleep" is not correct.