Phineas and Ferb in "the Digital World" is the 2nd episode of New Super Flynn-Fletcher Bros! In it, Irving is designing a Phineas and Ferb video game.
(Albert): What are you doing, Nerving?
(Irving): I'm designing a new Phineas and Ferb video game: P&F: The Duplicate World! In it, you play as Phineas, Ferb, or, if you beat the game, Perry. You have been teleported to an evil world where everyone but you is evil. You must outwit the villains and their Mominions! I've even made up a solution to the missing Perry problem where he's a secret agent! That's the bonus Perry Stage!
(Albert): Puhleeeasse! If you think that's a good game, wait'll (not real word :P) you see Super Jario Bros!
(Irving): Oh, for crying out loud! Anyway, it's finished! I'll post it on my blog!
Meanwhile, at the Flynn-Fletcher household...
(Irving, panting from running there): Guys! I just posted a new game on my blog! Let's check it out!
(Everyone else, with Isabella, Buford, and Baljeet): Yeah!
Meanwhile... Dooba-dabba-doo-ba! Dooba-dabba-doo-ba!
(Major Monogram): Hello, Agent P. Dr. Doofenshmirtz is illegaly modifying a virtual reality helmet. We want you to find out what's his new evil plan is, and put a stop to it. Good luck, Agent P!
Doofenshmirtz Evil Incorporated!
(Doof): Ah, Perry the Platypus! Your timing is uncanny, and by uncanny I mean COMPLETELY CANNY!
Doof pushed a button, dropping a cage on Perry.
(Perry): Growly noise thingy.
(Doof): You're just in time for my backstory!
Perry rolled his eyes.
(Doof): When I was a boy, my mother wouldn't let me play with my game console, the Game Man (get it? parody on Game Boy). It infuriated me. I could never play a video game since. So now I will force myself, and everyone else in the Tri-State Area, to "play" the video game of my choice! And I chose "P&F: The Duplicate World" because it caught my attention!
Meanwhile, back at the Flynn-Fletcher household...
(Irving): Let's play!
Just as they played, Doof hooked up his helmet to his "Very First Inator" (which connected to the Internet), and zapped a circle around the city, transporting everyone in the city, including Doof, into the video game.
(Phineas): What just happened? I felt a zap, but we're still here. Weird. But wait, there's the rollercoaster, the beach, the Spinning Tops of Doom, the race course (from the Beak), and everything else.
(Mom): How about some nice snacks?
(Candace): MOM! I don't know how all this stuff got back here, but here's ALL the proof!
(Mom): I know, isn't it wonderful?
(Candace): Wait a second! The REAL Mom would never let them do such dangerous stunts!
(Mom): Oh, sure I would! It shows how creative they are!
(Candace): Oh, well! I guess you're right!
Candace relaxed at the beach on a reclining beach chair thingy.
(Phineas): You know, I think you're not the real Mom!
(Mom): Let's have a talk inside.
They walked inside, only to find the place suddenly under lockdown, with Mom-headed snakes dropping from the ceiling.
(Irving [yes, he came in, too]): Gasp! Mombas! Deadly snake enemies I designed in my game! How'd they become real!
(Mom): Actually, the question is "How did you become digital!" You're in Irving's video game, and I'm a Mominion! Now, into the pits with you!
The Mominion threw them into a pit. Then they found themselves in a strange other world that looked like a huge version of Albert's room. Then they went through a dangerous world, battling the Momlings, the evil versions of themselves. But, just as they were about to defeat the evil Candace, she disappeared! Meanwhile, just before now with the Mominion and Candace...
(Mominion): Okay, Candace, how about you where these sunglasses!
She put them on, only to find something happening to her!
(Candace): What's going on? Aaaaaaaaaaa... Mwa ha ha ha ha ha ha ha ha ha ha ha ha!
(Mominion): You are now evil!
Because Candace turned evil, and because two evil or two good versions of ANYBODY can't exist in the same reality, the old evil Candace disappeared!
The gang arrived at a castle. Inside, they found a huge pit of soapy dishwater with a bridge to cross. A kitchen-knife-shaped switch at the end apparently was for destroying the bridge. Just then, a giant Mom-shaped creature dropped down onto the bridge.
(Mom-Shaped Monster): I am the Mom! You are apparently here to stop me! But I have a hostage, your now-evil sister, Candace!
(Buford): You won't get away with this!
He ran up to the Mom and jumped at her.
(Baljeet): Buford, no!
The Mom flicked him into the dishwater.
(Buford): Aaahh! I'm being washed!
(The Mom): Who's next?
(Everyone else but Phineas): Aaaaaaaaahhh!!!
(Phineas): I'm not scared! I know your weakness! Your lucky guitar pick!
He held it over the pit, threatening the Mom.
(The Mom): I guess I should tell you I'm not really the Mom!
She pulled off a mask, erasing a hologram that made her look like Mom, and showing that she, or HE, was really Albert!
(Albert): I'm Albert!
(Irving): Okay, Albert, I'm pushing the emergency boss shutdown button!
He pushed it, only to find that it didn't work!
(Irving): Oh, NO!
(Phineas): Gasp! Guys, I'm gonna flip the switch!
He tossed the guitar pick over Albert, but it went off course and hit something else.
But that started a hidden chain reaction that ended up flipping the switch! The bridge halves slid away from each other, each going towards its land end. This carried the gang to safety, but Albert got knocked off. Then he fell down, right to where Buford was in the water.
(Buford): Oh, boy.
Just then, the whole place disappeared, and they discovered themselves, with Albert, in Albert's bedroom.
(Phineas): What was that?
(Ferb): The world may never know.
(Phineas): Oh, there you are, Perry.
NOTE 1: To find out what role Perry played in freeing them, watch out for Perry the Platypus in "The Digital World!"
NOTE 2: Part of the inspiration of the plot came from the movie Scooby Doo and the Cyber Chase.