What does 니 mean?
Hi so I was trying to pick up some additional vocab and was looking through the lyrics of "no more dream" by bts and saw a line which went "얌마 니 꿈은 뭐니" and I had heard that "니" can be used as "cute" ending but in the context of a hip hop band that just didn't seem right. So I was wondering if there was some other meaning or if they really are using "cute" endings in their song?

Question

What does 니 mean?
Hi so I was trying to pick up some additional vocab and was looking through the lyrics of "no more dream" by bts and saw a line which went "얌마 니 꿈은 뭐니" and I had heard that  "니" can be used as "cute" ending but in the context of a hip hop band that just didn't seem right. So I was wondering if there was some other meaning or if they really are using "cute" endings in their song?

Answer

The exact meaning of "니" is "You". "니?" in ending is used for informal question instead of "습니까?, 됩니까?, 어요?"
For instance, 
                        (너) 어제 학교 갔니? (between friends or senior to junior)  
                        (당신) 어제 학교 가셨어요? (formal or junior to senior)
                        니 어제 학교 갔나?(between friends or senior to junior with southeastern Korean dialect)
                        It's the same meaning of "Did you go to the school yesterday?".