I grew up watching Avatar which is why I'm here. I specifically remember a character named minty (which obviously is incorrect due to the fact that I can't find) anyways I remember that he was with the gang and later betrayed them. I remember him being a young boy but I'm not entirely sure. Any help or answer will be greatly appreciated.
The first character that comes to mind is Jet or possibly another member of the Freedom Fighters. If it isn't any of those, you might want to take a look at Team Avatar#Enemies, which is a list of characters that were against Team Avatar at some point. Also, are there any features you recall that might narrow the character down (e.g. which nation they were from, which book they appeared in, what they look like)?