Formal:
* Dobranoc (doh-brah-nots) - This is the most common and formal way to say goodnight.
Informal:
* Dobry wieczór (doh-bree veech-or) - This literally means "good evening" but is often used as a polite way to say goodnight in informal settings.
* Dobranoc (doh-brah-nots) - You can also use the formal "dobranoc" informally.
* Na dobranoc (nah doh-brah-nots) - This is a more affectionate way to say goodnight.
Other Options:
* Spokojnej nocy (spoh-coy-nay-nay nots-ee) - This means "peaceful night" and is a more poetic way to say goodnight.
* Słodkich snów (swot-keeh snoof) - This means "sweet dreams" and is a very common way to say goodnight to children.
You can choose the most appropriate phrase depending on the situation and your relationship with the person you are talking to.