Bella the Platypus

Biography
Bella was taken from the Australian wild by smugglers. She was subjected to abuse and eventually had the abusers enjoyment of pain rub off on her. She became increasingly intelligent when an experiment her "owners" performed on her. She was able to use her intelligence to escape from her owners and make it to Ralsonville. She was found by a family in Ralsonville and they treated her very well. One night, she cut one of the children with her poisonous claw, He was in excruciating pain, but it didn't kill him. They took him in the hospital and discovered the poison wasn't strong enough to kill him. They soon saw the cut marks an the father noticed that the sides of the cut were made by an unusual pattern, a pattern that was on Bella's claw. It didn't take much time to surmise what had happen. The doctor wanted to poison Bella, but the family decided to dump her from the 6 story window. She miraculously survived, but sustained horrible injuries from the tree. She was left there to die until one week later, when Phineas and Ferb. They nursed her back to health but she didn't appreciate it at the very least, but she didn't show it, in fact she decided to stay with Phineas and Ferb even when they decided to return her to the wild.

Personality
Bella is a sadist who finds a pleasure in pain

Trivia

 * It's unknown how she made it to Ralsonville considering that Ralsonville is very vigilant and successful in their security efforts to keep their city concealed