Misperceived Monotreme

Sorry to be so harsh Agent P, but today is a very special day: Your one-hundredth battle with Dr. Doofenshmirtz!

Perry misses his 100th battle against Dr. Doofenshmirtz when Candace takes him to the Charity Pet Wash with her. Perry's absence goes unnoticed when the zookeeper's typical platypus at the Danville Zoo stops Dr. Doofenshmirtz's plan to zap his brother with his "Least Likely-inator." Meanwhile, the boys build a fun house Phineas and Ferb style.

Episode Summary
One day, while Phineas and Ferb were watching a report about the zoo's latest new animal, a platypus, the interviewers decide to to go see some other animals in the zoo. When they weren't looking, the platypus escapes into a truck, as it smelled a sandwich that was left in there. Meanwhile, Phineas and Ferb are thinking about making a fun house in the house and Candace gets a call from Jeremy. He was hosting a charity pet wash at the park. When Jeremy is talking about how a person's personality can be told by how they treat a pet, she took Perry to the pet wash.

At headquarters, Monogram and Carl prepare for the 100th battle for Agent P. When dumping out all the stuff for the fun house, the platypus got out and entered Perry's lair after Carl opened all the entrances. Mistaking it for the real deal, the platypus does Perry's job. At the pet wash, Perry tries to avoid getting bathed but failed. At Doofenshmirtz Evil Inc., the battle begins. Doof created a Least Likely-inator, which will make a person "do the least likely thing in their nature". On the side note, Irving got hit by it and tries to flirt with Isabella.

The battle starts with the platypus getting out of the trap. He licks up some spilled coffee, then crushes Doof with a sandwich display case. The sandwiches scatter on the Doctor's devices, who eventually got slammed into a brick wall. Perry is done bathing and is on the way home. After exploring the fun house, Doof shot the Least Likely-inator on Candace and exploded. Candace cleaned the whole thing up unintentionally before Linda got home. Meanwhile, the platypus left the lab and Perry arrived. Monogram and Carl congratulated him despite not fighting at all.

Songs

 * Quirky Worky Song
 * Livin' in a Funhouse

End Credits
Last verse of Livin' in a Funhouse

Whatcha doin'?
None.

Perry's entrance to his lair
Carl tests all the secret agent doors to see if any of them are jammed (Perry was late for his mission). The zoo platypus smells Carl's sandwich and instinctively walks into the tree elevator as it opens.

Evil Jingle
Doofenshmirtz Evil Incorporated!

Background Information

 * It is unknown if Carl, Monogram, and Dr. Doofenshmirtz found out that Perry never had his 100th battle with Doofenshmirtz.
 * This is the first season three episode to have more than one song.
 * This is the first time Jenny appears in an episode that Stacy does not appear in.
 * It is revealed that Doofenshmirtz's father is alive.
 * When Irving is hit with Dr. Doofenshmirtz's invention, he thinks that Phineas and Ferb's inventions are lame and he hits on Isabella.
 * If you look carefully when the platypus pushes the sandwich stand, he was on his hind legs like Perry, and his eyes were focused.
 * This episode reveals that Perry might hate baths. However, it's also possible he just wanted to escape and go fight Doofenshmirtz as quick as possible.
 * The logo to the O.W.C.A has finally been revealed in this episode.
 * The "Marsh" maneuver was most likely named after Jeff "Swampy" Marsh the creator of the show.
 * This is the first time that Phineas and Ferb's big idea is cleaned up by Candace.
 * Doofensmirtz was in the bathroom saying 'Shangri La', a Singapore hotel.

Errors

 * Along with "Ask a Foolish Question", most of the multiple line closed captions must be read from bottom to top instead of top to bottom.
 * It's unknown why Major Monogram, Carl, and Doofenshmirtz were unable to tell the difference between Perry and the Platypus that escaped from the Zoo. It may be colored that way so the audience can tell if it is a different Platypus.
 * When Candace picked Perry up whilst he was using his watch, in the next scene, the watch is gone.
 * In the opening scenes at the house, Perry doesn't have his top hairs, but while Candace is calling Jeremy, he has his top hairs again.
 * This is actually Perry's 118th battle with Doofenshmirtz (according to the list of episodes up to this point). we can also mention here that "Phineas and Ferb's Christmas Vacation!" in the future, also "Phineas and Ferb's Quantum Boogaloo", they hadn't fight in "Isabella and the Temple of Sap", and perhaps the events of "Unfair Science Fair Redux (Another Story)", count as the battle of "Unfair Science Fair", they hadn't fought in "Hail Doofania!", "No More Bunny Business", "I Was a Middle-Aged Robot", "Undercover Carl", "Traffic Cam Caper", "Perry Lays An Egg", "Thaddeus and Thor" and "The Monster of Phineas-n-Ferbenstein", also mention that "Phineas and Ferb Get Busted!" and "Wizard of Odd" were dreams, they hadn't fight in and which make a total of: 104 battles.
 * However, creators Dan Povenmire and Jeff "Swampy" Marsh confirmed the episodes don't take place right after the previous.
 * The mirror in the clip the O.W.C.A recorded was just triangles and a bit of Doofenshmirtz's hand and brush.
 * During the basement spin, the button on Ferb's shirt wasn't outlined.

Continuity

 * Fourth time someone other than Perry goes to fight Doofenshmirtz. The first was Peter the Panda in "It's About Time!", the second time was Planty the Potted Plant from "No More Bunny Business" and the third time was the Dodo Bird From "Last Train to Bustville".
 * Third time Perry doesn't interact with Dr. Doofenshmirtz. First is in "No More Bunny Business" and the second is in "Undercover Carl".
 * Second time Perry is referred to as a monotreme. ("Swiss Family Phineas")
 * The giant floating baby head is shown again.
 * This is also the 3rd or at least time the guy with the name Steve is shown ("The Lizard Whisperer")
 * Ticks and tocks are heard again ("Don't Even Blink", "Make Play", "Unfair Science Fair Redux (Another Story)").
 * Second time another platypus besides Perry is shown, though this time he is distinguishable from Perry, though only by his nose when he is smelling and his eyes, which are red. ("Oh, There You Are, Perry")
 * While Phineas is talking to Perry, the reporter can be heard telling the zookeeper that she had made the word "platypus" up, and then she said, "No, it's a real word." This is similar to a conversation Candace and Stacy had in an earlier episode ("Gaming the System").

Allusions

 * When Doofenshmirtz hits the brick wall, Monogram calls it the "Marsh Manuever". This is a reference to his voice actor, Jeff "Swampy" Marsh.
 * When Baljeet walks past the second last mirror in the Hall of Mirrors, he sees a monster-like version of himself. When he comes back, he is only stretched out, as the mirror normally would show him. This is the same in Disney Land's Haunted Mansion ride, only there are no fun house mirrors.

Cast

 * Vincent Martella as Phineas
 * Ashley Tisdale as Candace
 * Thomas Sangster as Ferb
 * Caroline Rhea as Mom
 * Mitchel Musso as Jeremy
 * Dan Povenmire as Dr. Doofenshmirtz
 * Jeff "Swampy" Marsh as Major Monogram
 * Dee Bradley Baker as Perry
 * Bobby Gaylor as Buford
 * Jack McBrayer as Irving
 * Lisa Ling as Takira Quawck
 * Alyson Stoner as Isabella