This is one criminally underrated Batman villain.
This is one of my favorite batman villains and she has only a little bit of screen-time. Also it should be pointed out that as soon as she reached the mirror her voice stopped being her usual childish voice and changed to what her voice would sound like at her own age.
Her name is Marion Louise Dahl and her body is unable to age past her childhood state. She made a living starring as a child star in various sitcoms, most famously Love That Baby. She was portrayed at 5 even though she was about the age of 20. Her character was named Baby Doll and was a trouble-making sweatheart whose catchphrase was "I didn’t mean to!" When she tried acting in other rolls than her character Baby Doll they all said her acting was atrocious. She was turned down after her character had lived out its charm on television and she was cursed to continue living as a child. Although she wanted to grow up, Marion couldn’t.
Here is a YouTube link to this scene so you can see how it really sounded.