"Aren't you coming down to the basement?"

Translation: Nem jössz le a pincébe?

[XeniaKuzav]

Why is it "jössz le" and not "lejössz"?

[jsiehler]

Because the nem needs to be right next to the verb stem in order to negate it. So the particle le has to be displaced to somewhere else.

[JohnWeber786406]

For questions, especially ones with interrogative words (Ki, Merre, Mi, Hol, etc.) - yes.
For nem/hanem sentences where verbs are compared, the prefixes remain attached. I am not going down, but going up - nem lemegyek, hanem felmegyek

[XeniaKuzav]

Thank you, it is clear now

[AlexusD90]

Negative proverbs don't exist? Only verbs with replaced at the end the indicator?

[BetsyLowe]

Thank you, Jacob!

[InaraCouto]

Thanks, Jacob.

[Joey412386]

How is it clear if you mean 1 person or a group? Both seems correct without a context in this case