Resolved questions
-니 at the end of a sentence

I think -니 is used to give a causal relationship between two phrases, like:

비가 오니 땅이 젖는다.
When it rains, the land gets wet.

But I have seen it at the end of sentences too, like:

내일 눈이 올 것 같니?
Do you think it will snow tomorrow?

Since there is no cause/effect connection here, I think -니 is just a casual ending used by people who are really close. 맞아요?