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
Phineas and Ferb are watching the news. The Danville zoo has a special about their latest new animal, a platypus that likes eating sandwiches. After debating whether "platypus" is a word, the interviewers decide to go see some other animals in the zoo. When they aren't looking, the platypus escapes into a delivery truck, as it smelled a sandwich that was left in there. Meanwhile, Linda calls Candace, telling her to do something instead of waiting for Jeremy to call her. Candace promptly gets a call from Jeremy. He tells her that he will be volunteering at a charity pet wash at the park. Candace shoos Perry out of the room, and continues her conversation with Jeremy. He comments that one can tell a lot about a person's personality by the way they treat animals, and tells her that she should bring Perry to the pet wash so they can wash him together. Candace reluctantly accepts.

Phineas suggests to Ferb that they add fun to everything. Ferb bends a piece of paper over his nose, making it look like a house. Phineas is inspired to make their house into a fun house. Perry's watch beeps, but before he can get to his lair as Agent P, Candace picks him up and announces that she's "borrowing" him. At headquarters, Major Monogram wonders where Agent P is. Carl makes himself useful by fixing Perry's hover chair, adding a hidden button so it will go to Doofenshmirtz's lair and come back automatically. He thinks Agent P's lair is kind of cute, since everything is platypus sized, "like kindergarten".

At the backyard, Phineas and Ferb accept their delivery of fun house materials. It happens to be the same delivery people as the ones who just delivered to the zoo. The zoo platypus, who was hiding in the truck, tumbles out with the fun house stuff and lands near the tree in the yard. Major Monogram is beginning to worry about Agent P, and orders Carl to open all the entrances thinking Perry can't get inside to his lair. Carl is eating his extremely stinky peanut butter, banana, and sardine sandwich as he does this, attracting the sandwich-loving platypus through the tree entrance. He lands in Agent P's chair, and Major Monogram, mistaking it for the real Agent P, tells the platypus that today is his 100th battle against Doofenshmitz. They planted hidden cameras all over Doofenshmirtz Evil Incorporated to watch all the action (and enjoy some cheap laughs). They even recorded hours of footage of Doofenshmitz singing in the bathroom. Monogram sends the platypus to his mission in the hover chair.

At the pet wash, Jeremy and Candace try to wash Perry. However, he refuses to go in the bathtub, and manages to squirm his way out of Candace's hands, taking refuge behind a tree. Jeremy finds him and hands him back to Candace, though Perry is still squirming.

At Doofenshmirtz Evil Incorporated, Doofenshmirtz turns off the news, now broadcasting about the missing platypus in the zoo. The platypus arrives and Doofenshimrtz also mistakes it for the real Perry. He quickly traps it and throws the remote onto the edge of a table. Doofenshmirtz shows him the Least-Likely-inator, which will make a person "do the least likely thing in their nature". He accidentally fires it, hitting Irving as he walks down the street with Isabella. He then does the least likely things that Irving would ever do: say that Phineas and Ferb are losers and flirt with Isabella.

Doofenshmirtz explains why he built the Least-Likely-inator: not only to make his daughter obey him and his father love him, but mainly to humiliate his brother in front of the legislature since it was the least-likely thing he would do. Apparently, Doofenshmirtz is hoping that this will cause the legislature to give the Tri-State Area to him, even though that's not how democracy works. The remote that trapped the platypus falls off the table, releasing the platypus. He starts to lick a spilled coffee on the floor.

Meanwhile at the Flynn-Fletcher house, Phineas and Ferb along with their friends are starting to make the house into a fun house. So far, there is a wall slide, a clown room, a cookie room, and a spinning basement.

The platypus is still licking the spilled coffee. Doofenshmirtz believes that he's using a fighting technique called "Singapore Crab", and then thinks that the platypus is playing mind games with him. The platypus sees the sandwich display case, full of sandwiches, and it runs to it and knocks it over to get to the sandwiches, crushing Doofenshmirtz in the process. The sandwiches scatter, landing on Doofenshmirtz's various switches and devices. The platypus looks as though he is about to attack Doofenshmirtz, but simply picks up a sandwich that is near his face. Doofenshmirtz runs toward the platypus, but it picks up another sandwich on top of a lever, deploying a brick wall that Doofenshmirtz runs into. Major Monogram says that this is called the "Marsh Maneuver", which he hasn't seen since 1974. Carl comments that Monogram had a perm back then, and Monogram retorts by telling Carl to stay off the internet.

Candace washes Perry, and Jeremy replies that "Perry's drowning in motherly love".

The platypus is still running around eating sandwiches, and narrowly escapes being squished on a table by Doofenshmirtz. Doofenshmirtz falls off the table and gets a pitcher of water poured on himself. The platypus eats another sandwich, opening the roof.

Candace and Jeremy take Perry home, only to discover everyone exploring the fun house. Jeremy thinks it's cool, while Candace obviously does not. Perry tries to get out, only to get lost inside a hall with never ending doors. They all land in Candace's room, which has become the cookie room. Candace is obviously aggravated, but she replies that she will come inside after getting the groceries out of the car.

Doofenshmirtz tries to zap the platypus with the Least-Likely-inator, but he throws a sandwich in the hover chair first. The platypus runs toward the sandwich and eats it, activating the automatic button. Doofenshmirtz tries to fire it at him before it's too late, but he turns it around too far, causing a cable on the machine to break and start spraying everywhere. The platypus rides the chair back to Perry's lair.

Meanwhile, Candace got hit by the Least-Likely-inator's final stray blast, causing her to clean the whole thing up unwillingly before Linda could see it.

The platypus leaves the lair and Perry arrives. Major Monogram and Carl congratulate him for his great work, calling him a star. Perry is confused since he didn't do anything.

Songs

 * Watchin' and Waitin' (instrumental)
 * Quirky Worky Song
 * Livin' in a Funhouse

End Credits
Last verse of Livin' in a Funhouse

What'cha 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 revealed that Doofenshmirtz's father is alive.
 * If one looks carefully when the platypus pushes the sandwich stand, he was on his hind legs like Perry, and his eyes were focused.
 * A part of the O.W.C.A.'s logo can be seen while Monogram and Carl are watching Doofenshmirtz. Also, when Perry lands on the chair in his lair at the end, Monogram mentioned the fight was a hit on the "'OWCA' internet".
 * The "Marsh" maneuver was most likely named after Jeff "Swampy" Marsh, the co-creator of the show.
 * This is the first time that Phineas and Ferb's big idea is cleaned up by Candace (though it was a result of Doofensmirtz's inator).
 * When Candace is cleaning up the fun house, the song plays backwards.
 * This episode along with "Ask a Foolish Question" was featured on the Phineas and Ferb The Movie: Across the 2nd Dimension (DVD) bonus disc in Toys R Us, and later on in The Perry Files DVD.
 * Ticks and tocks are heard again ("Don't Even Blink", "Make Play", "Unfair Science Fair Redux (Another Story)", " That Sinking Feeling").
 * 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").
 * Third time Ferb says the too young line. ("Vanessassary Roughness", "Canderemy")
 * 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")
 * This is the first time, however, "monotreme" is part of the title, but "monotreme" is not said onscreen.
 * 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")

International Premieres

 * July 25, 2011 (Disney Channel Brazil and Latin America)
 * July 28, 2011 (Family Channel)
 * October 3, 2011 (Disney XD UK)
 * October 9, 2011 (Disney Channel Asia)
 * October 16, 2011 (Disney XD Spain)
 * October 21, 2011 (Disney XD Germany)
 * November 12, 2011 (Disney Channel Portugal)
 * December 6, 2011 (Disney Channel Scandinavia)
 * December 17, 2011 (Disney Channel Bulgaria)
 * December 24, 2011 (Disney XD Poland)

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 Christmas Vacation!" in the future, also "Phineas and Ferb's Quantum Boogaloo", they hadn't fought 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" (also they didn't even fight in the Redux, they went to the store), 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.
 * As Doofenshmirtz looked outside, the color of the building was indigo but on the other scene it is now violet.
 * 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.
 * When Major Monogram tells Carl he's in the way the ear piece on Carl's glasses disappear for a moment.
 * When Candace says "Oh, there you are, Perry", Perry's arm with the watch on moves suddenly.
 * Before Phineas and Ferb look at their blueprints for the funhouse, Ferb's shirt button is missing.
 * When the platypus knocks the display case his eyes are focused, looking like Perry's.
 * While Phineas and Ferb is dancing with the Navy with wavy hair, Phineas's shoes turned black instead of blue

Continuity

 * The beginning of My Undead Mummy can be heard when we see the pet wash for the first time.

Allusions

 * Jeff "Swampy" Marsh - When Doofenshmirtz hits the brick wall, Monogram calls it the "Marsh Maneuver". This is a reference to his voice actor, Jeff "Swampy" Marsh.
 * Disneyland's Haunted Mansion - 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 Disneyland's Haunted Mansion ride, only there are no fun house mirrors.
 * Stitch! The Movie and Lilo &amp; Stitch: The Series - Both of these shows featured a character with a single-minded obsession for sandwiches.
 * Looney Tunes - Doofenshmirtz running into the brick wall is most likely a reference to cartoons like the Looney Tunes which is known to feature stuff like that.
 * Doofensmirtz was in the bathroom singing 'Shangri La', a famous hotel.
 * Apollo XVII mission - During the song Livin' in a Fun House a view of Earth is shown. This is the famous shot taken by the Apollo astronauts during the final mission to the Moon in 1972.
 * Syfy's House of Imagination - Candace and Jeremy discover everyone exploring the Fun House in the song  Livin' in a Funhouse a similar to Syfy's House of Imagination.

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, Additional Voices
 * Jeff "Swampy" Marsh as Major Monogram, Additional Voices
 * Dee Bradley Baker as Perry, Additional Voices
 * Bobby Gaylor as Buford
 * Jack McBrayer as Irving
 * Lisa Ling as Tykera Kwok, Additional Voices
 * Alyson Stoner as Isabella
 * Tyler Mann as Carl
 * Additional voices: Candi Milo, Corey Burton