On the inevitable 104th day of summer vacation, the season — and the series — is quickly coming to an end and it’s Candace’s last chance to bust her brothers, who build huge playground equipment for the finale of summer. She is quickly foiled, but when she goes to return a DVD to Vanessa and finds Dr. Doofenshmirtz's Do-Over-Inator, she finds an opportunity to redo the day, which results in other consequences like rips in the space-time continuum, the shortening of days and the disappearance of her brothers.

Tropes:

• Actor Allusion: At one point, Phineas and Ferb's invention gives the gang the live-action heads of their respective voice actors, as a tribute to their contributions to the series. Phineas becomes Vincent Martella, Ferb becomes Thomas Brodie-Sangster, Isabella becomes Alyson Stoner, and Baljeet becomes Maulik Pancholy. Buford, however, turns into an octopus. It was explained by the writers that this is because Bobby Gaylor, who voices Buford, is in his 50s, so putting a 50-year-old man's head on a preteen bully would seem weird.
• Aesop Amnesia: Like most episodes where Candace learns to relax and not obsess over busting her brothers, she eventually forgets this and is back to her busting attempts by the next summer. Likewise, Doofenshmirtz relapses into evil next summer, although it's revealed he stayed good for the school year, and "Act Your Age" reveals that he does give up his evil ways in the long-term.
• Ain't Too Proud to Beg: Upon learning that Doof has already won, Perry does this with a sad chatter, possibly to have Doof reconsider his new job as Tri-Governor and his anti-thwarting law. Of course, it didn't work.
• Armor-Piercing Question: Vanessa says one to her father about his new job as Tri-Governor of the Tri-State Area:
  Vanessa: I don't think this lifestyle choice is making you happy either, is it?
• The Bad Guy Wins: Dr. Doofenshmirtz manages to take over the entire Tri-State Area by creating a political position for himself known as Tri-Governor. To do so, he uses the time loops to trap Perry, builds up a Tri-State Governor's Mansion on top of City Hall, and puts up a voting booth to gain enough votes from the citizens to officially win the office. He even signs a legislation preventing Perry and the OWCA from thwarting him and his schemes until his term is over. Of course, this was the second time Doof succeeded in taking over the Tri-State Area, as the first time was in "Phineas and Ferb Save Summer".
  Doofenshmirtz: Everything's gonna be hunky-dory, 'cause I'm in charge, baby!!
• Bait-and-Switch: After Vanessa announces she is moving in with her mother, Norm plays the recording of her saying it back. Doof is in disbelief... that Norm has been surreptitiously recording them this whole time... and that Vanessa's moving out.
• Big Finale Crowd Song: As the Grand Finale of the whole series, naturally this trope would apply here. "Curtain Call/Time Spent Together" has the cast recapping some of the their major adventures with even Doofenshmirtz and Monogram getting in on the number, along with Phineas and his friends.
• Big "YES!": Doof does this twice, the first when he finally defeats Perry by putting in 30 traps to incapacitate him, and the second when he wins the election.
• Bookends: Perry, whose method of entering his lair to receive his mission was Different in Every Episode, uses a remote-activated door at the side of the house just like in the first episode.
• Call-Back:
  • "It's muffin time, sir!"
  • Candace returns Vanessa's French cinema DVDs, a call back to "Night of the Living Pharmacists" where Candace hung out with Vanessa's friends to watch French films. In the same moment, Candace wonders why in one of the films a mime kept letting go of a balloon, a nod to a similar gag done twice in "Summer Belongs to You!".
• Call-Forward: "Act Your Age" gets one during the Big Finale Crowd Song "Curtain Call/Time Spent Together", where after the line "Isabella kissed me but I got my mind erased" (referencing the events of Phineas and Ferb The Movie: Across the 2nd Dimension), Phineas tells Isabella, "you just wait ten years" accompanied by the clip of the two's Big Damn Kiss from the said episode.
• Chekhov's Gun: The spoon is the first object that disappears in the space-time. At the end Candace saves the day by throwing a spoon at the self destruct button of the Do-Over-Inator.
• Cloudcuckoolander: Isabella seems more distracted by the capri pants than by the severity of everything disappearing from existence.
• Commercial Break Cliffhanger:
  • Candace, Isabella, Buford and Baljeet getting sucked into a rift.
  • Phineas, Ferb, Candace, Isabella, Buford and Baljeet escaping from the void dimension.
• Continuity Porn: Being the show's final song, "Curtain Call/Times Spent Together" is full of this.
• Continuity Snarl: The first time Candace wakes up after Phineas and Ferb disappear from the timeline, her alarm clock somehow still has Phineas's voice on it saying, "I know what we're gonna do today".
• Dance Party Ending: The series closes out with all the characters jamming out while thanking the audience for watching.
• Dark World: Various objects, animals, and so forth vanish into an empty, gray version of Danville after they are Ret Goned away thanks to Candace and Doofenshmirtz messing with time and space.
• A Day in the Limelight: Candace and Doofenshmirtz take the spotlight in the finale, as their actions drive the plot of most episodes of Phineas and Ferb.
• Description Cut: With Candace, Phineas and Ferb stuck outside the timeline, Candace figures out their parents never had kids and assumes they now must have boring lives. The viewers get to see that their lives are anything but.
• Disney Acid Sequence: "No One I'd Rather Go Nowhere With", which takes place on Phineas and Ferb's big idea, and also "When Tomorrow Is This Morning Again", with the final shots of the latter paying tribute to "Busted", but with Doof in place of Vanessa.
• Distant Duet: When Tomorrow is This Morning Again is sang by both Candace and Doofenshmirtz.
• Door-Closes Ending: The final shot (as seen above) has Phineas wave goodbye to the viewers before closing the door.
• Dumbass No More: After spending 104 days on making many schemes that invariably fail on his part, Doof finally puts a scheme that goes to his favor on a grand scale. Given to the fact that he went through 23 time loops to actually learn from his mistakes, he made sure to carefully set his traps for Perry in case the latter would try to escape from them one-by-one. And when Perry is finally trapped (offscreen), Doof wastes no time in creating the Tri-Governor's mansion and putting up a voting booth to gather enough votes to legally win the office and sign up a law forbidding O.W.C.A. to thwart him again. Also, prior to his Heel–Face Turn, he already made sure that the Do-Over-Inator has a Self-Destruct Mechanism, which the kids utilized in order to stop the time loops for good.
• End-of-Series Awareness: The title of the special itself alludes to the show ending.
• Eye Am Watching You: Done by Candace to the boys as everyone goes inside at the end, which is followed by a smile and point.
• Fold the Page, Fold the Space: Candace and Doofenshmirtz accidentally trap the world in a "Groundhog Day" Loop and notice that the day gets shorter with every loop, erasing parts of the world in the process. Baljeet explains this phenomenon using a paper towel. He uses a hook to rip a strand from the paper towel, representing the disruption in the time-space continuum, and keeps ripping the paper shorter and shorter until nothing is left. His conclusion is that, left untreated, the time loop will eventually whittle down the universe into nothingness.
• Good-Times Montage: Of a sort. During the "Times Spent Together" song, The gang (including Candace) reminisce about the awesome summer they had, while Doof, Perry, Vanessa, and Norm have their own reminiscing session. What they are saying is obscured by the song, but their miming seems to make clear which adventures they are talking about.
• Graceful Loser: Upon seeing that Doof has succeeded in becoming Tri-Governor, both Monogram and Perry are very miserable as they cannot touch Doof anymore and that Perry himself will be suspended from work thanks to Doof's new anti-thwarting law. Despite this, Monogram states that he and the rest of OWCA will have to live with it until Doof's term is over; even Perry is willing to do the same as he happily encourages Vanessa to come clean with Doof about her intent to join OWCA's internship program.
  Monogram: (to Perry) So I guess we're the bad guys now. And I guess this means you're on hiatus, at least until his term is over. Monogram out.
• "Groundhog Day" Loop: For Candace and Doofenshmirtz, who were both inside the -inator's bubble upon its activation, so they both relive the last day while still retaining their memories.
  • Of course, actual groundhogs end up being sucked into one of the time rifts.
• Heel–Face Turn: Doofenshmirtz gives up evil for good in this special; even Norm does the same as well. Even "Phineas and Ferb: Act Your Age" and Milo Murphy's Law made it clear that it stuck. However, the Season 5 revival reveals that while this stuck for the following school year, Doofenshmirtz returns to evil the following summer.
• I Shall Taunt You: Doof does this on his brother Roger after being elected as Tri-Governor:
  Melanie: (on the intercom) Pardon me, Mr. Tri-Governor, the Mayor's on the line.
  Doofenshmirtz: Put him through. Hello, Roger!
  Roger: (on the intercom) Heinz, did you steal my secretary?
  Doofenshmirtz: Yes... yes, I did.
  Roger: (on the intercom) What makes you think you can do a thing like that?!
  Doofenshmirtz: Well, it's easy.... because I'm the boss of you! Nyah!
• In the Style of: "We Gotta Get Back in Time" is done in the style of Rubber Soul-era The Beatles.
• Internal Deconstruction: This special deconstructs Doofenshmirtz's life goals. As Vanessa points out, Doof wasted the entire summer creating schemes to take over the Tri-State Area in order to assert that he's evil, when in actuality, he's only doing this due to being bitter and petty about his hilarious yet tragic childhood. She also pointed out that his successful goal of becoming Tri-Governor has brought no happiness to him either. Realizing this, Doof decides to rethink over his life by retiring from evil, and spends the rest of the day with Vanessa, Norm, and Perry.
  Vanessa: Dad, you're totally missing the point. You spend all of your time working on your ridiculous inators and I can't—
  Doofenshmirtz: Okay, first of all, they're not ridiculous. Convoluted and ultimately pointless, maybe.
  Vanessa: Oh, come on, Dad, you build them just to exact petty revenge trying to prove you're evil.
  Doofenshmirtz: What? I'm evil. I-I am evil!
  Vanessa: No, Dad. You're basically a nice guy who's pretending to be evil. And, you know, it seems like it's all out of obligation to your backstories, not something that truly comes from your heart.
• Knighting: When the gang builds the catapult to get back into Danville, Buford dubs it "the Buford van Stomm Time Catapult".
  Buford: I won the naming rights fair and square.
• Landslide Election: What Doofenshmirtz accomplishes by posting up a voting booth after trapping Perry and creating the Tri-State Governor's Mansion:
  Doofenshmirtz: Now I just gotta get someone to vote for me... anyone actually, 'cause I'm running unopposed.
• The Last Title: "Last Day of Summer" is the subtitle, with emphasis on the word "last".
• List Song: The final song has the kids mentioning some of the adventures they had.
• Literal Metaphor: When Buford says he has "some notes" on Phineas and Ferb's ultimate ride, Phineas says "Back to the drawing board!" Ferb then pushes a button that turns their enormous structure into an actual drawing board with a blank blueprint on it.
• Locked Out of the Loop: Literally invoked on everyone during the time loops, with the exception of Doofenshmirtz and Candace as they were inside the bubble when Candace first activated the Do-Over-Inator. Eventually subverted with Phineas, Ferb, Isabella, Baljeet and Buford when they end up in the void.
• Motor Mouth: Candace goes a mile a minute when trying to explain to her mom who Phineas and Ferb are after they disappear.
  Candace: YouseelaterontodaywhichiskindalikelastmonthtomevanessasdadinventsthisthingwhichhesaysdoesntworkbutitactuallydoesbecausewellhereiambutitalsodoesntworkbecasuetheyrenotheresoeventhougheverydayrepeatesnoteveryoneoreverythingrepeatsbecauseYOUDONTEVENKNOWWHATCAPRIPANTSARE!!!
  Linda: "Capri pants"? Is that a boy band?
  Candace: They're... (facepalms) Gah!
• My God, What Have I Done?:
  • Candace is horrified when Phineas and Ferb are pulled out of existence, and even moreso when she learns the time loops are becoming smaller, to the point where all existence will eventually vanish, all because she activated Doof's machine out of desperation.
  • Doofenshmirtz gets into this when he realizes that even with his machine gone and after accomplishing his goal, the rifts are still erasing things from existence and that the time loops are becoming quicker that would destroy the space-time continuum.
• Nap Inducing Speech: Buford gets annoyed upon hearing Baljeet explain ripples in the space-time continuum.
  Buford: Oh, PLEASE stop talking!
• No Fourth Wall: The song "Curtain Call/Time Spent Together" breaks the fourth wall in various ways. The characters acknowledge events that occurred in the series that they normally would not know about, such as the events of "Phineas and Ferb Get Busted", "Across the 2nd Dimension","Night of the Living Pharmacists" and "Act Your Age". Isabella is surprised by the last part. The song also has the characters singing to the audience, thanking them for watching. At the end of the song, Phineas waves goodbye to the audience before closing the door. During the song, Phineas also mentions that "Unfair Science Fair" has "two parts".
• Non Sequitur: When Doofenshmirtz mopes about how Vanessa is going to move out and live at Charlene's house full-time, Norm randomly says "I like pancakes!"
• Noodle Incident: After it is revealed that Norm has been secretly recording whatever Doof and Vanessa say, he plays three past incidents of what may have caused Vanessa to move out. And they are hilarious!
  Doofenshmirtz (on tape): Hey, Vanessa, hand me that cadaver!
  Doofenshmirtz (on tape): Honeybun, if you go to the living room and see a pile of skin flakes, just ignore it.
  Doofenshmirtz (on tape): I know you said the time machine in the bathroom was a bad idea, but if you need to go, you should do it last week.
• Oh, Crap!: Happens a lot:
  • Candace notices that ever since she activated the Do-Over-Inator, time rifts are erasing things from existence, including spoons, oranges, tigers, and tragically of all... her brothers. And the worst part is that no one even noticed or even acknowledged their existence.
  • Doofenshmirtz himself comes to the same mindset upon attempting to turn off the Do-Over-Inator after accomplishing his goal, only for a time rift to suck the -inator away. He even finds it more appalling to see that even when the machine gone, the time rifts are still erasing more things away from existence, especially snowglobes.
  • Mayor Roger falls into this upon learning that Doof has won enough votes to become Tri-Governor.
  • Perry falls into this upon learning that he's no longer allowed to thwart Doof anymore due to the latter's anti-thwarting legislation.
  • In the void, the kids react in horror when they learn that the time loops are getting quicker and when Candace admits to having activated the Do-Over-Inator. Even when they manage to return to Danville with the machine, they can't be able to deactivate it because the loops are going too quick... that is until Candace cues in the Chekhov's Gun.
• Orphaned Punchline: When Candace approaches Buford, Baljeet, and Isabella, Buford is somehow attempting to convince Isabella to buy him a new hat.
• "Pan Up to the Sky" Ending: Done just before the final musical number.
• Poor Communication Kills: Fed up with her father's refusal to take time away from his evil scheme for a conversation she insists is important, Vanessa announces that she's moving out. Rather than hear his daughter out in subsequent iterations of the loop, Doofenshmirtz only pushes her away harder in order to endlessly refine his latest attempt to take over the Tri-State Area, convinced that she'll change her mind about leaving if he succeeds. It's not until he does succeed that she finally gets him to listen to her and clarifies why she wanted to move out: not because she's angry at him, but because she wants to join OWCA's internship program and their living together would create a conflict of interest.
• Prove I Am Not Bluffing: Having succeeded in becoming Tri-Governor, Doofenshmirtz revealed to a furious Perry that he just drafted and signed a legislation declaring it illegal for anyone to thwart the Tri-Governor until his term is over. At first, an unimpressed Perry believes that Doof is bluffing, but Doof refutes this by showing the signed legislation paper, which left Perry shocked and depressed.
  Doofenshmirtz: Go ahead, read it, it's all perfectly legal. Look like your thwarting days are over, Perry the Platypus.
• Puppy-Dog Eyes: As stated from above, Perry looks back at Doof and chatters sadly at him, possibly begging him to reconsider his new job and anti-thwarting law, but Doof refuses by literally calling out the trope.
  Doofenshmirtz: No, no, don't give me the puppy dog eyes, you're gonna make me cry. Sheesh!
• Race Against the Clock: At the climax, Candace is stuck in a loop where she and her friends return the Do-Overinator to the timeline, only for it to be too far away to reach before the loop point, which is becoming shorter and shorter by the loop, while Doofenshmirtz has completed the Time-Straighten-Outinator, but wastes valuable time being Mr. Exposition.
• "The Reason You Suck" Speech: Vanessa gives one to Doofenshmirtz by pointing out that his successful goal in becoming Tri-Governor doesn't convince her that he's a "successful" villain. Granted, it's less about tearing Doofenshmirtz down and more about convincing him that he's better than he thinks he is, but Vanessa does make the point that his "evil" is more an obligation to his "tragic" backstory than actually being truly evil.
• Recycled Animation: Some animation of Phineas and Ferb and Isabella playing their instruments is reused from "Phineas and Ferb Save Summer"
• Recycled Soundtrack: When Isabella sees Phineas and regains her memories of him, the background is the same as "Act Your Age" from when the two had The Big Damn Kiss.
• Regained Memories Sequence: Zig-zagged. Isabella and Baljeet regain their memories of Phineas and spoons when they are sucked into the alternate dimension. Buford expects it to happen to him with oranges, but it doesn't.
• Ret-Gone: A secondary effect of the Do-Over-Inator not only causes a persistent "Groundhog Day" Loop, but also causes sporadic rifts in the space-time continuum that swallow up things, causing people to forget those things ever existed; after a spoon (and, somehow, all spoons) is taken, people resort to eating cereal out of the bowl, whereas when Phineas and Ferb are taken away, they're completely forgotten. Since Doofensmirtz and Candace were right by the Do-Over-Inator when it activated, they remember everything that was taken, and also remember the previous time loops.
• Riddle for the Ages: "But we're still baffled by the Giant Floating Baby Head."
• Ripple-Effect-Proof Memory: Since Candace and Doofenshmirtz were in close proximity of the Do-Over Inator, only they have memory of the things that were erased from existence and the previous time loops.
  • Downplayed with Phineas, Ferb, Baljeet, Isabella and Buford, as they have no idea what is happening until they end up in the void, where their memories catch up and finally understand the effects about the time loops and rifts.
• Sequel Hook: Vanessa got an internship at OWCA, and at the end, she tells her father that OWCA was searching for a few good animals. Since Doof was raised by ocelots, that makes him a good candidate. This is followed up with in "The OWCA Files" with Doof being a new recruit, but Vanessa is not shown interning and instead, Carl is still seen working there despite supposedly having left for college.
• Series Fauxnale: As the title states, it's the last day of summer which was the season the series was set in, and thus the final episode. However, it became a Fauxnale when the series was renewed for two additional seasons in 2025.
• Shout-Out: "You there, boy! What day is this?"
• Slipped on the Wheels: this is the first thing happening to Candace after her getting up. And multiple times too, as that day later gets repeated in a time loop.
• Spotlight-Stealing Squad: Despite being the Series Finale, the episode is more focused on Candace and Doofenshmirtz. Somewhat justified in that the previous episode tied up Phineas and Isabella's plot line as well as that of most of the other main characters, with the exception of Candace and Doofenshmirtz — the latter of whom was revealed to have had a Heel–Face Turn, which we see here.
• Strange Minds Think Alike: When Baljeet realizes the loop point is becoming shorter, he uses a hook and a piece of paper to explain it to his friends. Later on, Doofenshmirtz says he'd use those things to explain if he had them, implying that the hook and paper were erased from existence.
• Subverted Catchphrase: When Isabella finally remembers Phineas, she simply says, "Hey, Phineas!" but she does not say the other two words of that catchphrase.^note Whatcha doin'?
• Tempting Fate: When Doofenshmirtz's plan to become Tri-Governor works, he decides to deactivate the Do-Over-inator to prevent it from undoing his victory but it gets sucked out of the timeline before he has a chance to. Doof then hopes that the inator won't be able to cause time loops where it is. Cue the next time loop.
• Thanking the Viewer: The song "Curtain Call/Time Spent Together" has the characters singing to the audience, thanking them for watching. At the end of the song, Phineas waves goodbye to the audience before closing the door.
• Then Let Me Be Evil: Vanessa points out that Doofenshmirtz indulges in his evil schemes only because he feels obligated to do so by his horrendously difficult childhood.
• Those Two Guys: Buford and Isabella fill this role in between P&F disappearing and everyone else being sucked into the alternate dimension. (Normally, Buford and Baljeet fill these roles.)
• Throw the Dog a Bone: After spending the entire summer making schemes that invariably fail (save for a few successful ones), Doofenshmirtz finally gets one right by taking over the Tri-State Area and usurping his brother, right before he reconciles with Vanessa during the time loops, and even thinks he saved the day by fixing up the time stream (though it was really Candace, since the -inator to fix the loops wasn't plugged in, but Perry never reveals this to him).
• Took a Level in Jerkass: After Phineas and Ferb are ripped from the timeline, Isabella, Buford, and Baljeet (particularly the former too, as Baljeet is focused on the space-time continiuam) become a lot edgier with each other. Buford becomes more irritable and Isabella acts like she couldn't possibly care less about what anyone else is talking about. It really reinforces the two brothers as the heart of the group.
• Victory Is Boring: Despite Doof being happy that he accomplished his goal, he eventually reaches an epiphany that his success didn't bring him any happiness as he expected, as he had to spend most of his work schedule signing more legislation papers.
  Doofenshmirtz: Who would've thought being Tri-Governor would be so involved?
• Whole-Plot Reference: The episode combines the plots of Groundhog Day and The Langoliers.
• Writers Cannot Do Math: Cosinus equal to 17 is by definition an impossible result.
• Yank the Dog's Chain: Downplayed, as though Doofenshmirtz finally takes over the Tri-State-Area, his victory becomes moot when the Do-Over-inator undoes it. However, Doofenshmirtz already felt that his victory didn't bring him any happiness and has had his Heel–Face Turn while reconciling with Vanessa, so he doesn't really care.
• You Are Too Late: Doof gave one to Perry as he signed a law forbidding any O.W.C.A. agent to thwart him until his term as Tri-Governor is over, which left Perry extremely depressed.

Aaron Daniel Jacob: It's just about the time we spent together,
It's just about the time we spent together...
With you.