Okay. I have two characters one can definitely be an enemy, and another that can be a friend or enemy, depending.
Alyss Summers- She's a typical girl that thinks she's the best, people hate her, she's powerful and she acts like a pureblood to try and hide that she's actually a half blood. Her lifelong dream is to be the Dark Lady when she's older, and she believes that anyone else who is not a Slytherin should be terminated, immediately. She doesn't have any friends just 'acquaintances' and she has more enemies than those. Others are fearful of her, even some older students are, as she has learnt a few spells from the older students. She is pretty much one of the rulers of the first year. When you get there, she'll be a second year.
Then there's Rosemarie Wilkinson- She's a Ravenclaw, who at first wanted to be a Slytherin, but she's more qualified for Ravenclaw. She loves reading but she's fearful of being called a nerd so she hides it. She's a bit mean, compared to Alyss she's like the tooth fairy, but she'll take a while to warm up to you. She doesn't have many friends because of that because most people don't want to bother warming up to her. She loves shopping, and she acts like a plastic like girl, but in reality, she's a girl that you'd want for a friend because she'd stand up for you, but only if you take the time to warm up to her.
PM me if you're interested. 
Sophie is sort of occupied with planning a wedding at the moment... 