Danielle "Dani" Phantom is an unstable, female clone of Danny Fenton/Phantom, created by Vlad Plasimus in his quest to create the perfect half-ghost "son". Originally sent by Vlad to capture Danny, Danielle wound up siding against her creator after Vlad revealed his true colors. After preventing Sam and Tucker from getting into trouble with their folks (they stole Fenton equipment to go rescue Danny from Vlad), Danielle departed for parts unknown.
As Danny's clone, Danielle looks exactly like Danny save that she's younger, has longer hair in a ponytail and of course is a girl. Danielle also has Danny's ghost powers, save for his cryokinesis and his Ghost Wail. However, due to her status as a clone Danielle's DNA is unstable. Prolonged usage of her ghost powers can result in breakdown, causing her to melt into ectoplasmic goo. As long as she doesn't use her powers (or use them to their full extent), Danielle can retain her form.
Disclaimer: Dani Phantom is from the cartoon Danny Phantom, and is the property of Butch Hartman and Nickelodeon. She appears here solely for the purpose of role-playing in milliways_bar, from which no profit whatsoever is being made.