The clones of Danny were created by Vlad as failed attempts to create the perfect half-ghost son. The main clone, the only one not mindless, and the only one to survive, is Dani Phantom.
They first appeared in "Kindred Spirits." Vlad wanted the perfect half-ghost son, but instead he got several failed ghost clones and a daughter, Danielle. Besides her, the clones were a Bed Sheet Ghost (revealed to be a skeleton when uncovered), a muscular and tall monster-like ghost, the tiny ghosts who later revealed himself to be a deformed version of Danny, and a prime clone.
All of the clones, except for Dani, dissolved into ectoplasm. They all served Vlad as if he were their father, but Dani later realized she was just "a mess that Vlad's not going to clean up." She teamed up with Danny to defeat Vlad and left afterwards.
Dani reappears in "D-Stabilized." She is running away from Vlad, and is searching for Danny so he can stabilize her, but both of them end up being caught by the mayor's assistant, Valerie Gray.
Vlad was attempting to catch and melt Dani so that he could study her ectoplasmic remains in order to make a perfect clone, but fails, thanks to Danny and Valerie (who thought that Dani was the villain and Vlad Masters was a victim). Danny managed to stabilize her with the "Ecto-Dejecto," and she once again flew away.
Dani can be seen in "Phantom Planet."
By duplicating a subject's DNA, it is possible to create a living duplicate of the specific organism. The clone's body might not be completely identical to that of the original, but the clone will have some qualities of the original.
Vlad's chalet is the only place known to use cloning technology. These clones are grown in large containment units.
The Bed Sheet Ghost, with his bed sheet removed, is a black skeleton torso with red eyes.
The Monster Ghost is a tall, muscular clone with gray skin, a black mohawk, green eyes, and sharp teeth. He wears a black collar around his neck and a black cuff on each wrist, all with green studs, and wears ripped black pants and no shirt.
The Tiny Ghost appears as a neon green dot or a small silhouette when tiny. Up close, he has fangs and appears to be melting away. After he overshadows Danny, he looks exactly like him up until he dissolves into ectoplasm.
The Prime Clone is an exact duplicate of Danny. He has Danny's white hair, green eyes, and tan skin, and wears his usual black-and-white jumpsuit with his signature logo on the chest.
Dani Phantom has the same color scheme as Danny for her appearance. She has white hair (black in her human form) pulled back into a ponytail and green eyes (blue in her human form), and wears a black-and-white two-piece jumpsuit that's similar to Danny's suit, complete with the same logo on her chest.