Bunny is the temporary fourth Powerpuff Girl in the episode “Twisted Sister.”
In the story, Blossom, Bubbles, and Buttercup try to create a sister who can help them handle their demanding superhero schedule. Their experiment produces Bunny, a kind and powerful character with a different appearance and limited ability to speak clearly.
Bunny’s Chemical X formula is imperfect, so she has difficulty understanding ordinary language and controlling her powers. Despite this, she attempts to help the original trio and demonstrates genuine compassion. The episode ends tragically when the unstable formula causes her to disappear after restoring the people she had transformed.
Bunny is not an official permanent member of the team. The episode deliberately presents her as a temporary fourth sister, which distinguishes her from recurring characters such as Princess Morbucks and the Rowdyruff Boys.