Is 너 casual?
Yes! It's only used among close friends or for people younger than you
Yes
What is the difference between 너희 and 너?
너희 is used when you address more than one person and 너 is used for a single person.
Someone pls answer
"너, 나와!"
Informal
당신! I just had to get it out of my system. XD Amazingly it was accepted. XD