It's a rainy day; Phineas and Ferb's plans have been cancelled, and the power has gone out. So to pass the time, Ferb's Grandpa Reginald recalls the tale of one of his ancestors creating a platypus monster.
Meanwhile, the power is out in Doofenshmirtz's building as well, and Dr. D. has been locked inside. When Perry comes in and accidentally locks himself in with Doofenshmirtz, Doofenshmirtz tells him the story of one of his ancestors, who created a concoction that would turn him into a monster.
Tropes present:
- Affably Evil: Dr Jekyll Doofenshmirtz's idea of being evil includes doing pranks such as ding-dong-ditch and pretending to catch someone's nose and telling someone to give a high five only to pull away when they slap them.
- Affectionate Parody: To Frankenstein, The Strange Case of Dr. Jekyll and Mr. Hyde, and their movie adaptations from the 1930s.
- Big Blackout: The lights went out in the entire city as Grandpa Reg starts his story.
- Breaking the Fourth Wall: Candace complains about the story being told in black-and-white, causing the scenery to shift to bright, saturated colors. Phineas then pops up and says, "Perhaps muted color would be better"; the scene then shifts to muted color.Grandpa: Who's telling this story, anyway?
- Breathless Non Sequitur: "...and that's why there are pumpkins." Said by Grandpa Fletcher as he finishes his story about a giant platypus monster.
- Call-Back: Ferb's only line at the end of the episode is a parody of the very first line he ever said in "Rollercoaster".Ferb: Platypus monsters are the only monsters to lay eggs.
- Content Warnings: The episode opens with one, as a Shout-Out to the Universal Horror version of ''Frankenstein''. Later, Major Monogram does a similar one, although he explains the curtains behind him as the storm causing water damage and his tux as being late for his cousin's wedding.Phineas: Good evening, ladies and gentlemen. We thought it only fair that the show you're about to see may disturb you. It may shock you. It may even horrify you!Ferb: (spits out hairball)Phineas: You've been warned.
- Ding-Dong-Ditch Distraction: Dr. Jekyll Doofenshmirtz does this after transforming into a monster.
- Else World: What will become the first of several for this series.
- Framing Device: The story is framed by Reg telling it to the boys during a summer storm, and Doofenshmirtz telling Perry a similar story that overlaps Reg's.
- Generation Xerox: Somehow, the dynamics of Phineas, Ferb, Doofenshmirtz, and everyone else's ancestors are very similar to their own. Phineastein and Ferbgor created a big thing (in this case a huge platypus monster), Constance attempts to bust them to the angry mob (as a stand-in for "Mom"), while Dr. Jekyll Doofenshmirtz's schemes are thwarted by the giant monster platypus, and Constance's attempt to bust the duo are undone by Dr. Jekyll's scheme.
- Halloween Episode: The second of such.
- Hiroshima as a Unit of Measure: Parodied:Phineas: How big is [the monster], Grandpa?
Grandpa: Bigger than a refrigerator, but smaller than a really big refrigerator. - Identical Stranger: Dr. Jekyll's butler Jameson looks exactly like Roger, but has a different voice actor.
- Inventional Wisdom: Dr. Jekyll's Concoction-Brewinator he created to turn himself into a monster for some reason has a fairy princess setting, which he lampshades when he questions why he made that setting in the first place.
- Poke the Poodle: During the "He's Evil-er" number, Dr. Jekyll Doofenshmirtz as an evil monster pulls all manner of childish pranks, like teepeeing a house and playing ding-dong ditch.
- Punctuated! For! Emphasis!: "I'm...telling...mob."
- Record Needle Scratch: When Candace complains about the story being in black-and-white.
- Right Behind Me:Constance: How are you gonna enter the Best Monster Contest? You don't even have a monster.
The platypus monster stands behind her and growls.
Constance: He's right behind me, isn't he? - Special Edition Title: This is the first episode to have its own special title sequence.
- Suspiciously Similar Substitute: Instead of calling a mother referred to as 'Mum', Constance calls the angry mob to bust Phineastein and Ferbgor. She even refers to the angry mob as 'mob' just like how Candace refers to Linda as 'Mum'.
- Tempting Fate: A random man wearing just his underpants walks into his balcony proclaiming that he's finally cured of his Absurd Phobia of having a giant platypus see him in his underpants. Cue the platypus monster passing him by as it rampages through the city.
- Toilet Paper Prank: Jekyll Doofenshmirtz does one during "He's Eviler".
- Torches and Pitchforks: Jekyll Doofenshmirtz tries to get an angry mob's attention in order to increase his credit as a mad scientist. Meanwhile, Constance tries to get the mob to see Dr. Phineastein's platypus monster.
