I can offer you my First Year Slytherin, Lily Fossil/Livia Delaney as an enemy.
Lily/Livia, is a well mannered girl. Who enjoys fashion a lot and looking her best is her top priority, apart from dance which she is the best in. She is graceful and loyal to her friends as long as they are loyal to her. She's nice at times, but generally pretty mean to about everyone. But is at this moment making more of an effort to make friends, even if she's false and/or pretending to like the person. Lily/Livia can appear trustworthy but really doesn't trust anyone. She hates the fact she's a witch but this will slowly change as the year progresses.