Cormorant

He meant the end for Batgirl--just not in the same way as Joker was. Cormorant was the complete opposite of Killer Moth who was, in all actuality, a really cheesy villain. Cormorant was a serious threat on the other hand, almost killing Batgirl at one point. He made her seriously contemplate her role as Batgirl and, after defeating him, she had finally decided to put Batgirl behind her. It would be the Joker that would ensure her never being able to have second thoughts on that decision...