What a fun, creative movie.
Here's a brief summary of the movie:
Bruce Wayne takes on Weapon X.
Weapon X shoots two fingers off Bruce's hand, and steals his manservant Alfred.
Bruce Wayne, in a moment of heterosexuality, steals Weapon X's girl.
Weapon X turns to David Bowie to create a teleportation machine, and as a side benefit receives a surplus of top hats.
In the end, Alfred helps the mirror universe Bruce to kill Weapon X in a factory that apparently produces water-logged Wolverines.