Buford has lost his goldfish while swimming out in the ocean, so Phineas and Ferb build a submarine and help him search for it.

Meanwhile, after accidentally saving a kitten, everyone thinks Dr. Doofenshmirtz has now become a good guy, to his annoyance. He decides to build the Media-Erase Inator to prevent the news channels from rebroadcasting the footage of the kitten rescue.
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!!Tropes
* AccidentalHero: Happened to Doofenshmirtz when he saved a kitty. He actually tripped on a curb and the kitty just fell into his shopping bag.
* ArtisticLicenseBiology:
** Biff the goldfish is able to survive in the deep sea, despite being a freshwater fish who would shrivel up and dehydrate due to osmosis in salt water.
** Also, the final scene of the GoodTimesMontage shows Buford sleeping with Biff; Biff's eyes are closed, when in real life, fish don't have eyelids.
* BaitAndSwitch: The Media-Erase-Inator doesn’t erase Candace’s photographic evidence; it causes a truck to crash into a water tower, and the ensuing flood destroys her camera.
* BigNo: When Buford first realized that Biff was missing.
* GiantSquid: One attacks the gang after they find Biff. Buford has to face his fear and fight it off.
* GoodTimesMontage: Buford has a flashback to all the wonderful times he had with Biff, set to the song "Fish Out of Water".
* HeelFaceTurn: Everyone ''thinks'' Dr. D did this. He wants to clear up the misunderstanding.
* HelpImStuck: Buford briefly gets stuck in the entrance of the submarine.
* HulkSpeak: Buford does this when he spots Biff in the ocean:
-->'''Buford:''' Buford love Biff.
* InelegantBlubbering: Buford cries copiously over his lost goldfish while on the search.
* InsistentTerminology:
** Buford isn't crying over his lost goldfish, he's "[[SandInMyEyes sweating from [his] eyes]]".
** Subverted when Isabella asks him if he's sweating through his eyes, and he says "No! I'm just crying!!".
* LeaningOnTheFourthWall: After the submarine was built, Ferb said the construction took "at least a montage."
* PrecisionGuidedBoomerang: Perry uses his hat as one of these.
* TemptingFate: Just as Candace makes it home with the camera and says, "Finally, I got those boys!", she is submerged by a huge flood of water from the water tower, ruining the film.
* TestYourStrengthGame: As a child, Buford played one of these at a carnival. He hit it just hard enough to win a goldfish (which, funnily enough, is below "Nothing" and "Next to Nothing" on the scale), which he named Biff.
* WeWantOurJerkBack: Even ridiculously-tolerant Phineas is annoyed by Buford being a total crybaby.
* WhatHappenedToTheMouse: We do not get to see what happens to the submarine after the kids make it back to shore.