In the ongoing storyline “Death of the Family,” the Joker becomes convinced that Batman’s sidekicks have made him soft, so he vows to destroy the Bat-family. The punchline is that Batman will be the one that kills them!
The Joker presumably accomplishes this by turning Batman’s allies against him, which won’t be difficult now that he’s discovered their secret identities, including Batgirl AKA Barbara Gordon.
In Batgirl #14, the Joker kidnaps Barbara’s mother and proposes with her wedding ring while it’s still attached to her severed finger! The wedding will take place January 16th in Batgirl #16.