As told in Batman: The Dark Knight #23.1 - A Rising Star of Red!
Shauna was born a twin. Her twin brother Ferdie was beloved by everyone, including her concert pianist father and ballerina mother. While Ferdie was given special treatment by everyone, from casting director to the other children, Shauna was abused, teased and sometimes forgotten all together.
One day while being teased, Shauna learned she could move things with her mind. She used these new found powers to murder one of her tormentors. She would later use these powers to kill her twin, and make it look like an accident.
Shauna was trying to find her place in the world when she first meet Ferdie, the dummy. She saw him at a birthday party, killed the clown who was using him.
Shauna would later go on to kill her parents and start doing ventriloquist acts that would usually end with a dead audience.
Major Story Arcs
For more information see: Harley Quinn Annual
Shuana makes her way into Harley Quinn's dream when she gets a face full Cannibisylocibe 7-A.
The Ventriloquist (Shauna Belzer) was created by Batgirl writer Gail Simone and artist Fernando Pasarin. She made her debut in Batgirl #20.