Potter Puzzle

My first is in bane but not in foe;
My second in Harry and Malfoy, too;
My third starts a small golden ball, you know;
My fourth isn't we or they or you;
My fifth is in Slytherin but not Gryffindor;
My sixth's in the window but not in the pane;
My seventh's the shape of a snake on the floor
And my last is in ark but not in rain.
My whole is a monster, at Hogwarts fought,
Whose death brought the Dark Lord's plans to naught.