This is the list of Big Ideas in Season 4.

Episode Image Big Idea Disappearance Notes
"For Your Ice Only" Hockey fieldFYIO Everyone say Canadian BaconHockey z9 The boys create Hockey Z-9. An ice resurfacer hit by Doofenshmirtz's Abominable-inator clears the Z-9 course away.

This is similar to Football X-7 from "My Fair Goalie".

They saved the name "Y-8" for croquet.

"Happy New Year!" The New Years Ball The boys plan their own New Year's Eve ball drop , complete with a customized multi-dimensional ball. Ferb launches the ball into outer space, and it explodes into fireworks. This was inspired by Vivian, who wanted to stay up and watch the ball drop. The ball drop is also inspired by the Times Square Ball Drop in real life.
"Fly On the Wall" A Tire Swing
Sundae Machine
A giant rocket-powered tire swing. Buford presses a red button that reads "FLY", and it goes up into the sky. When the tire swing disappeared, Phineas moves a certain lever and it becomes a sorbet machine.

if a certain lever was pulled, it would emit a beam that would turn a human (specifically Candace) into a fly.

"Bully Bust" Dental hygienosphere The Dental Hygienosphere, a tooth-themed amusement park ride. Buford is hit by Doofenshmirtz's Luffa-Plex-Dill-Pickle-inator and sent into orbit; his shoelaces get caught on a stray decoration, taking the ride with him. The ray pulls Buford up with the ride.
"My Sweet Ride" Tumblr mh7ttwrNoE1rmra37o1 500 The boys restore and trick out Lawrence's old car for Candace. The car doesn't disappear, in fact, Linda and Lawrence see it but they think that was Lawrence the one who made it. The car won Best in Show at the Doo Wop Hop.
"Der Kinderlumper" Rutabaga vehicles The boys created rutabaga-themed vehicles for the Running of the Chinchillas. The vehicles were trampled by the oversized chinchillas. All the kids were also trampled, but unhurt.
"Sidetracked" Phineas asking where Perry is in the episode Sidetracked The boys build a metal superstructure. Not seen, but the superstructure is carried away by a magnetized cloud. The invention is not seen in the episode.
"Primal Perry" Infinite probability generator Baljeet has problems with making the right choice, so the boys make a machine to help him. Liam's giant Boomerang destroys the machine thus reverting Baljeet back to only himself. When Baljeet had to make a choice he would be copied into two Baljeets and then three Baljeets and so on.
"Mind Share" Mind Share title cardMindSharePromoTwo The boys build a mind share device. Satellite: N/A

Mind Share Machine: Morg and his friends made it self-destruct.

After seeing a commercial of Morg in taking a vacation into another planet.
"Backyard Hodge Podge" Hodge Podge invention revealed They make an invention out of recycled parts. Doesn't disappear, but Candace can't see it clearly when zapped by Doofenshmirtz's Eye Fog inator while Linda thinks she's hallucinating. The invention uses parts from past ones.
"Bee Day" Giant wading pool Phineas and Ferb create a giant wading pool for their Mom and friends. The pheromones end up landing on the giant wading pool, and the swarm of bees, attracted to the pheromones, lift the whole thing into the air. The bees pop the pool. As Candace's old wading pool, the only part unaffected. Inspired after Linda seen some kids playing in a wading pool.
"Bee Story" Bee Story-Isabella and the sorbet machine Isabella borrows the sorbet machine that will turn her and the Fireside Girls into bees. Does not disappear, but after a few hours the effects wear off and they become themselves again. The Fireside Girls needed to earn their Bee Keeping Patch.
"Great Balls Of Water" The gang having fun They make a giant water ball. The water ball hits a prickly sphere, causing all the water to be released into a hole. Inspired by Baljeet in physics camp about water surface tension.
"Where's Pinky?" I can smell the future They amplify Buford's senses to those of a dog. Buford runs into the City Hall, where he eventually takes it off. Don, a City Hall tour guide is later seen running out of the edifice with the helmet on. Inspired by Isabella, who has lost her dog.
"Knot My Problem" Gordian Knot They make a giant replica of the Gordian Knot[[ ]] out of licorice.. Candace is zapped by the stray gun of Doofenshmirtz's All-You-Can-Eat-Buffet-Inator, causing her to eat the entire project. N/A
"Just Desserts " The kids started climbing They create a giant rock climbing wall out of lawn clippings. A swarm of bent-bill knot-hatches pick the wall for nest material, demolishing it.
"La Candace-Cabra" We present to you, the cupra-copter They set off to search for a rare Chupacabra by using their Chupa-Copter. The Chupacabra is actually an animal agent, Agent CH, so Perry uses the Switch Place-inator, making it switch places with Buford, and it flies away on the Chupa-Copter. Inspired by Buford's grandfather hunting the Chupacabra.
"Happy Birthday, Isabella" Birthday for Isabella revealed They throw a birthday party for Isabella. Doesn't disappear, but the grand finale gets turned into butterflies.

The grand finale was not seen, but part of it was mentioned (laser light show and swans).

All Isabella wanted for her birthday is to be alone with Phineas.

"Love at First Byte" NŚLAWSEMR The boys created a laser light show for the grand finale of the block party. Norm's head clings to the PHLASER and flies off to space before it was scheduled to do so. N/A
"One Good Turn" One Good Turn Isabella, Ginger, Buford, Baljeet, Candace and Stacy compete in an event created by Phineas and Ferb. Doesn't disappear, but the jumbo-tron with Phineas and Ferb gets zapped with Doofenshmirtz's 90-Degree-Turn-Inator, causing it to block Linda's view of the entire project. For doing this project, Phineas and Ferb use the leftover building materials that remained after making the invention in Backyard Hodge Podge.
"Phineas and Ferb: Mission Marvel" Surfing AsteroidsSatelitaCandace and isabella headed up to the space station1373048682000-128907-0051Mqdefault (54)The heroes getting their powers back In the beginning of the special, Phineas and the gang use the satellite from their space-station to power up their rocket-powered surfboards to surf the asteroid belts. Later, they build a Secret Hideout for Emergency Defense (or S.H.E.D. for short) full of machines to help the Marvel superheroes get their powers back. It is never explained what happened to S.H.E.D., but Candace accidentally makes the space station crash down to Earth, and Doofenshmirtz disintegrates it with his Disintegrator-inator. N/A
"Thanks But No Thanks" Mqdefaultpiramid The boys create a series of pyramid-related sports. N/A
"Troy Story"

Isabella and Phineas in a chariot
Trojan War
Screen Shot 2013-08-25 at 1.22.47 PM

Phineas and Ferb recreate the Trojan War. The flying chariots get tangled up with the Trojan Dinosaur, and they fall onto the castle, crashing everything. Later, Lawrence gets zapped by Doofenshmirtz's De-Clutter-Inator, causing him to clean up the wreckage. This was originally supposed to be the big idea in "I Scream, You Scream", but was cancelled due to Isabella having her tonsils removed.
"Druselsteinoween" Haloween party in Drusselsteinian castleDjFerb The boys host a giant Halloween party N/A N/A
"Terrifying Tri-State Trilogy of Terror" Armed with bubble washers They accidently make evil platypus clones by pouring grape juice on Perry, so they use bubble washers to take them out. The entire adventure was a story.
"Face Your Fear" A view of foam town The boys created "Foam Town " as a safe place to skateboard without having to worry about getting hurt. The bat Derek flies through "Foamtown" multiple times causing Doofenshmirtz's head to hit it time and time agian, eventually causing the giant bolt to come out and foamtown to roll away to the desert. N/A
"Cheers for Fears" Scrapbook-aganza page 5 They make the Scrapbook-Aganza , a giant scrapbook with Candace and Jeremy's moments, as a present for Jeremy's birthday. Candace gets hit by Doofenshmirtz's Worst-Fear-inator, making her state her worst fear is that the Scrapbook-aganza will fly away before Jeremy arrives. It does exactly that. Candace couldn't figure out what to get for Jeremy, so she asked Phineas and Ferb to make this.
"Just Our Luck" The stating point for sky tennis Phineas and Ferb decide to create Sky Tennis. After the effects of the Stinklekrampen-Inator wear off due to Perry destroying it, the contraption sinks into a crack in the Earth after Candace said that it is not like this would happen. The idea of Sky Tennis is similar to that of Jetpack Volleyball from the episode "Sleepwalk Surprise"}
"Return Policy" Extreme batting cage Phineas and Ferb create the ultimate baseball challenge. After Buford hits all the levels in the cage and the ball goes into the target, jet packs come out of it and carry the ultimate batting cage away and then it explodes into fireworks.

Phineas decides to create the create the ultimate batting challenge after Baljeet mentions that hitting a baseball involves the basic principles of velocity, force, and geometry.

They also made a giant water slide at Aqua Maximus.

"Live and Let Drive"
Lald035 seriously, they're enlarging DNA
Lald039 who's giant foot is that
The big idea was only reduced to a Funny Background Event, but it somehow involved getting DNA out of a pool, and a giant human foot
"Phineas and Ferb Save Summer" We're joining you to celebrate around the world Phineas and Ferb make a tribute-to-summer concert and also save it using a giant rocket engine. N/A
"Father's Day " S04E21 Samolot Phineas and Ferb build a biplane for his father Doesn't disappear, but Reg flies it away before Linda and Candace return.
"Imperfect Storm" You start by blowing a bit of wind Phineas and Ferb make a wind amplification machine to fly enormous kites. A storm hits and the kites are destroyed.
"The Return of the Rogue Rabbit" TROTRR5 They help the fireside girls with their puppet show by creating a giant marionette fireside girl puppet. Agent P uses it to fight Dennis the Rabbit, eventually destroying it.
"It's No Picnic" Picnic Power! The boys construct a picnic-themed amusement park in Danville Park The entire thing and the people there-except Isabella and Phineas-are sent home by the Transport-inator. Isabella was trying to make use of a day when Ferb had a dentist appointment to spend time alone with Phineas, but fails after Ferb is hit by a ray from the Transport-inator, sending him back to the backyard.
"The Klimpaloon Ultimatum"
Klimpaloon, Phineas and the gang
They try to help Love Händel to find Klimpaloon
"Operation Crumb Cake"
The boys construct a large art piece out of various things in their kitchen drawers. Phineas comes into contact with a beam from the Un-Retrograde-inator and he undoes the crestion.
Phineas and Ferb create a machine for change the smell of the air
"Phineas and Ferb: Star Wars"
Phineas holding the Death Star disk

In a galaxy far far away from Summer, the counterparts of Phineas and Ferb try to return the blueprints of the death star to the rebels.

During the song they also fix evaporators, train rats and do several things.

Doesn't disappear, by the way, they return the plans.
"Lost in Danville"
A mysterious capsule falls into their yard and they use Ferb`s Z-ray machine to investigate it. A ray from the Unexist-inator hits the black hole, which has already sucked in the capsule and its residents. This adventure is set in another reality; at the end of the episode, the original Phineas and Ferb are watching the whole strange scene through a portal from the sorbet machine that turns people into flies and bees.
"The Inator Method"
Baljeet after winning the digital trophy
The boys make a model solar system racing tower. A man buys it.
"Night of the Living Pharmacists" The gang by the Rubberization Ray

Phineas and Ferb build a Rubberization Ray and use it to give their skin rubber like qualities.

Later, they make a pulley and a giant sprinkler to stop the Doof zombies.

The Doof Zombies destroy the Rubberization Ray.
"Tales from the Resistance: Back to the 2nd Dimension "
Discovering Sports
The alternate version of the boys play sports and they also try to rescue Perry-2 This episode happens in the 2nd Dimension
"Doof 101"
Phineas and Ferb make modifications in their school yard
"Act Your Age "
Fireside Girls, Ferb and Baljeet admire their romantic dinner
Toddler Phineas and Isabella in backyard
Preschooler Phineas and Isabella in backyard
Kid Phineas and Isabella in backyard
Tween Phineas and Isabella in backyard
The teen Fireside Girls, along with Buford and Baljeet, set up a romantic dinner to set Phineas and Isabella together. Also, in a flashback montage, Phineas is seen building a giant robot as a baby, a popcorn machine as a youngster, a generic machine at about the same age he is in the main series, an oversized can opener as a teenager, and a giant robotic eggplant as an adult. The date is taken away by a rolling dumpster.
"Last Day of Summer"
First incarnation of the last big idea

Phineas and Ferb try to seize the last day of summer by doing "everything".

Then they use a machine to get back in time.

There were so many ways it went, they are unknown, but Phineas and Ferb ended up being erased from existence. The last Big Idea.
"The O.W.C.A. Files" None None Phineas and Ferb only appear in the credits.
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