It's a rainy day, and Phineas and Ferb's plans have been cancelled, as well as the power. So to pass the time, Ferb's grandpa Reginald recalls the tale of one of his ancestor's creating a platypus monster.
Meanwhile, the power is out in Doofenshmirtz's building as well, and Dr. D has ended up locked inside. When Perry comes and locks himself in too, Doofenshmirtz tells him the story of one of his ancestors, who created a concoction that would turn him into a monster.
- Affectionate Parody: To Frankenstein, The Strange Case of Dr. Jekyll and Mr. Hyde, and their movie adaptations from Universal Horror.
- Big Blackout
- Ding-Dong-Ditch Distraction: Dr. Jekyllshmirtz does this.
- 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.
- Poke the Poodle: During the "He's Evil-er" number, Dr. Jekyllshmirtz pulls all manner of childish pranks, like teepeeing a house and playing ding-dong ditch.
- Punctuated! For! Emphasis!: "I'm...telling...mob."