Moonstone would be a great enemy for Spider-Man in terms of how opposite they are. For one, Moonstone is motivated primarily if not solely by selfishness, whereas Spider-Man, driven by his sense of responsibility, has consistently sacrificed his own chances of happiness and success to save lives throughout his time as a hero. For another, their relationships with their mothers; Peter thinks the world of his Aunt May (she raised him, she counts as his mother), while Karla disdained and ultimately murdered her own mother so she wouldn't find out that she was a supervillain. A confrontation between them playing on those traits would be interesting, especially if he found out she was currently the head psychologist of Ravencroft.