Animals

Animals in Phineas and Ferb
Though Perry is the only animal with a major role within the show, appearances of a wide variety of mammals, fouls, reptiles, and amphibians reaccure throughout many of the episodes, often involved with Phineas and Ferb's Plans, Doofenshmirtz's schemes and inventions, and O.W.C.A..

Perry the Platypus
Perry the Platypus, codenamed Agent P, is Phineas and Ferb's pet platypus who, unknown by his owners, lives a double life as a secret agent for the O.W.C.A. (Organization Without A Cool Acronym), which is primarily composed of animal spies. He is the star of the B - Plot within the show, and only Major Monogram, Carl, the Intern, and his nemesis Dr. Heinz Doofenshmirtz know of his identity. Candace occasionally sees Perry as an agent, but dismisses it as her mind playing tricks on her. Phineas and Ferb have seen Perry as an agent only once, but thought he was a toy that was made by mistake. ("Toy To The World") Perry is an inspiration to many of his owners' ideas.

Bucky
Bucky is the former pet dog of the Flynn-Fletcher Family. He is thought to be the pet before Perry came along. Bucky's remains are fossilized in Danville's Natural History Museum. ("It's About Time!")

Suzy's Poodle
The Johnson Family Poodle is Suzy Johnson's pet, whom she trained herself to be particularily aggressive toward Candace. The poodle can be seen terrorizing Candace in "One Little Scare Ought to Do You Some Good!" and "Interview With a Platypus"

Biff
Buford's pet goldfish Biff, was won at a carnival and defending his pet was what converted him into a bully. He briefly lost and recovered Biff in "Voyage to the Bottom of Buford"

Goldie
Phineas and Ferb's pet goldfish Goldie was an inspiration for them to build a backyard aquarium to prevent her from getting lonely. When the tank was frozen and Candace knocked it out of the backyard, Goldie was set free into the ocean along with the other marine animals. ("Backyard Aquarium")

Steve
A chameleon pet of Ferb's, Steve, a logically reasoned name because he looks like a Steve, grew to a gigantic size because of an invention of Doofenshmirtz, but eventually returned to his usual small size. ("The Lizard Whisperer")

Dennis, a.k.a., Mr. Cutie Patootie
Formerly a O.W.C.A. agent, Dennis is a rabbit on a mission to inflitrate Perry's lair and steal the system of the agency. It was Perry's mission to stop him and Candace adopts him as a pet, names him Mr. Cutie Patootie, and gives him access to their house. ("No More Bunny Business")

Pinky the Chihuahua
Pinky, also known as Agent Pinky and sometimes Agent P, is Isabella's pet chihuahua and works for the O.W.C.A., but in a different division than Perry. His nemesis is Professor Poofenplotz. ("Isabella and the Temple of Sap")

Peter the Panda
Peter the Panda works for the O.W.C.A. and was Perry the Platypus' replacement nemesis for Dr. Heinz Doofenshmritz. He teamed up with Perry to defeat Heinz and Perry later again became his nemesis again. ("[[It's About Time!")

Only Son
Only Son was Doofenshmirtz's father's award winning dog. Heinz loathes the dog for not being able to bring back the family garden gnome, forcing him to stand in the yard for hours at a time as the gnome. ("Got Game?")

Nosey
The feared Lake Nose Monster, also known as Nosey, lives in Nose Lake and was Phineas and Ferb's friend on their visit when they agreed not to expose her existance. ("The Lake Nose Monster")

Mr. Fluffypants
Mr. Fluffypants, also known as Mr. Cat, is Heinz Doofenshmritz's cat that he finds on the street and adopts. He names him Fluffypants after his uncle.

O.W.C.A. Agents
Other agents besides Perry appear in the show, mostly un-named, including a bear, chicken, dog, frog, kangaroo. mouse, owl, eagle, raccoon, whale, hedgehog, goose, and a deceased turkey.

Doofenshmirtz's Inventions and Schemes
A couple of Heinz's evil schemes revolves around animals, including dogs, pidgeons, cats,whales, termites, and cloned Perry the Platypuses.

Phineas and Ferb's Big Ideas
A couple of Phineas and Ferb's Big Ideas revolves around animals, including cats, dogs, birds, fish, dolphines, whales, an octupus, a giant squid, snakes, mice, hamsters, elephants, and horses.