The correct word is "멋있어", which is 멋(cool, chicness, flair) + 있어 (has, is). So it means "It looks great" or "You look awesome" (context determines "you" or "it"). The last "ㅇ" could be a mistake, but it could also be intentional. Many Koreans (especially youths) tend to distort spellings like this to add nuance or humor. It might make things interesting to them, but more difficult to new learners.

멋있엉 = 멋있다 Pretty, beautiful ; cool