Wikia

Phineas: "What do you think the scariest thing was, Ferb?"
Ferb: "Definitely the giant floating baby head."
Phineas: "Yeah.....yeah, where did that come from?"
-On the baby head.^[src]

The Giant Floating Baby Head is a mysterious being that appears very randomly. While he/she tends to appear in some of Phineas and Ferb's Big Ideas, both Phineas and Ferb are clueless as to where he/she comes from.

Victorian times

In Victorian times, an identical baby head entered the Best Monster Contest. It is not known if the baby head has been around for hundreds of years, or that was just a lookalike ("The Monster of Phineas-n-Ferbenstein").

Present life

The giant floating baby head first showed up when Phineas and Ferb tried to help Isabella get rid of her hiccups by building a haunted house in the backyard. After Candace went through the haunted house to find her brothers, she complained about how outrageous the house was and asked why the giant floating baby head was even there. The baby head cried after Candace told him/her to be quiet. He/she was also in the haunted house's elevator when Candace was going to use it and was abruptly told to leave the elevator. At the end of the day, Phineas and Ferb relaxed in the tree and thought about what the scariest thing they did was, and Ferb stated that it was the Giant Floating Baby Head. They both suddenly wonder where it came from anyway ("One Good Scare Ought to Do It!").

The baby head showed up again as one of the supplies being delivered to the Flynn-Fletcher house when Phineas and Ferb build the monster truck arena in their backyard to help Candace learn how to parallel park although it was not in the arena or in/on the monster truck. ("It's a Mud, Mud, Mud, Mud World"). He/she reappeared on a handcart behind the boys and Candace when they built the PF 5000 Animatron. The baby head was shown being lifted upwards ("Out of Toon").

The baby head was also one of Chez Platypus's customers and was allowed by Buford into the restaurant ahead of Candace and Jeremy ("Chez Platypus"). He/she was also behind Candace's window as Candace was talking to Stacy about her text message to Jeremy. The baby was being carried by a lever for unknown purposes ("At the Car Wash").

He/she visited Heinz Doofenshmirtz when his foot was broken, and somehow managed to sign his cast. He/she was accompanied by Dr. Bloodpudding at the time ("The Bully Code"). He/she is briefly seen in Livin' in a Funhouse, in the line "The bathtub is your bed and a floating baby head" ("Misperceived Monotreme").

He/she was among the various people in Phineas and Ferb building. Before the building's completion, Phineas mentioned putting something next to a giant gorilla head, which is most likely a reference to this ("The Doof Side of the Moon"). The baby head was also seen during the song Carpe Diem ("Rollercoaster: The Musical!").

Numerous giant floating baby heads of various sizes appeared in the 4th Dimension during Brand New Reality, maybe that's where they come from ("Phineas and Ferb The Movie: Across the 2nd Dimension"). Months after summer, on Halloween, someone had a baby head costume, he/she was shown a few moments ("That's the Spirit").

Then, the baby head, appeared as an implement for constructing the tower ("Escape from Phineas Tower"). In Candace's mind, he/she appeared in the song Going Deep into Your Mind, as the fact, that Candace is afraid of the baby ("Monster from the Id").

Candace was briefly transformed into the Giant Floating Baby Head after she was accidentally transformed into a fly ("Fly on the Wall").

Background Information

The giant baby head came, according to Dan Povenmire, "one board panel drawn by Mike Diederich and one of our directors, Rob Hughes thought it was hilarious and made a whole bit about it. Now it shows up all the time."^[1]
"Oil on Candace" had a giant baby in it. However, it is not the same as the giant floating baby head as the Baby had a body as well as a different skin color and facial structure.
A mechanical giant baby head appeared in "Put That Putter Away".
The baby head is seen in the Phineas and Ferb video game.
In the song Technology vs. Nature during the line "when a child cries out in the night, it's rarely for the washing machine" an identical baby with a different hair color is shown.
As of "Misperceived Monotreme" and all its subsequent appearances, the baby head's eyes are more oval shaped rather than the circle shaped eyes seen in previous appearances.
The Giant Floating Baby head appears in the Camp version of the online game Summerizer, behind the mountains when you combine Perry and Agent E.

Appearances

"It's a Mud, Mud, Mud, Mud World" -Appeared as a thing for constructing the mud race.
"Its A Mud World After All" (Spot the Diff) -Appeared when Buck Buckerson took the mud track in Spot the Diff.
Toy to You and Me" (Spot the Diff) - Appeared replacing a Shimmy Jimmy toy for a few seconds.
"The Monster of Phineas-n-Ferbenstein" - Appeared in the monster contest, possibly as a contestant of the Best Moster Contest.
"One Good Scare Ought to Do It!" - Appeared in the Haunted House. Candace commented that it made no sense being there, and later shooed it at of an elevator. At the end, Phineas asked Ferb what he thought the scariest thing was. Ferb decided on the Giant Floating Baby Head, and Phineas realizes that he didn't know how it got in the Haunted House.
"Out of Toon" - Appeared, wheeled by on a dolley, when constructing the Phineas and Ferb Studios.
Phineas and Ferb (video game) - Appears in a bonus game.
"Chez Platypus" - Appeared while floating to Chez Platypus, and Buford lets him in, to annoy Candace.
"At the Car Wash" - Appeared, while carried by a crane, in Candace's window while constructing the car wash.
"The Bully Code" - When Major Monogram shows some security photos of Doofenshmirtz Evil Incorporated from early in the morning, the Giant Floating Baby Head appeared with Dr. Bloodpudding. Then Dr. D's cast has a message from him.
"Phineas and Ferb Hawaiian Vacation" - Appeared running from door to door while Phineas and Ferb follow the Aqua Primates in the hotel.
"Wizard of Odd" - Appeared three times. First while Candace was dreaming in the start. Second as a globe in Bustopolis. And third in Candace back to reality in the end.
"The Doof Side of the Moon" - He was floating behind some rails while Phineas and Ferb finished Albert's tour of the Biggest Tower.
"We Call it Maze" - When Candace pulled the rope through two ways of the Maze, it floating through the two ways, somehow connected to the rope.
"Rollercoaster: The Musical!" - Appeared in the grand final of Carpe Diem.
"Misperceived Monotreme" - Appeared in the Funhouse in a checker-themed room where Ferb is using a bathtub as his bed.
"Take Two with Phineas and Ferb: Neil Patrick Harris" - Neil Patrick Harris uses his magic make Ferb dissapear, and when he tries to make him reappear again a few times, one time he makes the Giant Floating Baby head appear, but he soon proceeds to make it dissapear.
"Phineas and Ferb The Movie: Across the 2nd Dimension" - When the 1st Dimension Gang is travelling through dimensions to escape some Norm Bots and return to their dimension, in a lot of different sizes, in the 8th Dimension.
"That's the Spirit" - A kid trick-or-treating as the Giant Floating Baby Head walked by a while behind Isabella as she told Phineas about her costume.
"Escape from Phineas Tower" - A construction Worker pushed the Giant Floating Baby Head on a dolley past a sleeping Candace to the Unescapable Tower.
"Monster from the Id" - Appears in the song "Going Deep into Your Mind" looking at Candace, also at the end of the episode, where Buford stays in Candace's mind.
"Mom's in the House" - The Perrytronic transformed into it during its test run.
"Sleepwalk Surprise" - Appears in Doofenshmirtz's dream.
"Ferb TV" - It appears in a show called The Klimpaloon and Giant Floated Baby Head Hour, along with Klimpaloon.