It's Christmas time in Toonville, so Bloo and various other characters are gathering and preparing to celebrate. But little do they know that the Pumpkin King is out to conquer Christmas, and he's bringing some monstrous help.
Bob and Larry prologue
It's almost Christmas in Nashville, Tennessee and the narrator introduces Bob the Tomato, president of the BlooJ's Foster's Home for Imaginary Friends fan club, is deep in preparations for the holiday. With the help of his unenthusiastic assistant, Larry the Cucumber, Bob the Tomato sets pictures of Bloo, Mac, Jenny, Eric Cartman, Homer Simpson, SpongeBob and The Eds on the mantelpiece, puts up his various Bloo-themed ornaments, and bakes Christmas cookies which Larry eats near the end of the prologue Bob also takes time to open a letter from a fan, who asks if Bloo likes Christmas as much as he does. Bob remarks that there was once a time when Christmas in Toonvile was unheard of and it was also the time where Christmas was almost canceled forever and decides to tell the tale.
"It's a Foster Christmas? ACT 1"
The story begins with a narrator introducing us to the story. He states that the story took place in the world of BlooJ. He then asks if we've wondered where The Bloo has been. And if not, we should begin. It then shows Patchy the Pirate who opens, revealing the story.
We then go to Halloween Town, where Jack Skellington is less than happy due to finding out that his Halloween special for the year has been cancelled. However, Zero gives Jack a poster for BlooJ's upcoming Christmas Special. Jack laughs evilly as he starts to cook up a fiendish idea.
Meanwhile, in Toonvile, Bloo prepares to sneak up on Jenny and take her by surprise with a Karate attack. Upon approaching the Treedome, Jenny is putting up Christmas lights, which Bloo mistakes for a fire and tries to put it out with a fire extinguisher. After recovering from the drenching, Jenny is shocked to find out that Bloo has never heard of Christmas and tells him all about it.
Later, Bloo is at Foster's talking about Christmas with Mac, Wilt, Edwardo, Coco, Spongebob and Shrek explaining the story of Christmas. While Mac, Wilt, Edwardo, Coco, Spongebob, and Shrek are excited about the matter, Mr. Herriman is being his usual, uncaring, grouchy self, and expresses disbelief, saying he can't believe that people would celebrate a holiday where "a jolly prowler breaks on your house and leaves." This causes Bloo to burn him in response.
Back in Halloween Town, Jack is talking with the band in Town Hall, where he plays to them a rock solo on his bells. The band tries to emulate this, but all that comes out of them is a terrible sound that is so loud, it blasts the mayor out of the building and into the camera.
The Mayor then calls for next person to try to get the job. Sally then shows up. Jack request help from her. Sally, however, does not want any part of Jack's Christmas, as she explains to the skeleton that she's had a vision about Christmas involving smoke, fire, and a mysterious silhouetted figure with glowing white eyes. Jack takes this in stride, however, as he asks Sally to make him some crack for his Christmas. Sally refuses, calling out Jack for being an ass. In response to this, Jack kicks Sally into a pit, 300 style, before he decides to go make the crack himself.
Meanwhile, back in Toonvile, Bloo and Mac have set up a machine to launch the bottled letters to the North Pole for Santa Claus. After explaining what it does, Bloo goes about asking the denizens of his hometown what they want for Christmas. These include new hats for Stan Marsh, Kenny McCormick, Kyle Broflovski, and Eric Cartman, a new Foster's episode for the Eds, and a decent lawyer for MermaidMan and Barnacle Boy, just to name a few.
At the same time, Jack continues the preparations for taking over Christmas in his Tower. As the Mayor pulls up to the tower in his car, Jack is smoking his crack and tripping balls, imagining himself as a gingerbread man being eaten by a giant reindeer before being pooped out as an egg that is broken, causing multiple Mario Heads to fly out.
Back in reality, the Mayor tries to get Jack to come out of his house by telling him he has weenies, but the Pumpkin King refuses. When the Mayor continues to insist, Jack throws a sheep with his head on it at the Mayor through his window.
In Toonvile, Mac pops out of the ground in a cemetery to ask what Bloo wants to do now. Bloo, who also comes out of the ground, says he wants to summon Santa with a song. The two then promptly start singing as they go about their work, including decorating homes, shopping for presents, and even setting up a large Christmas tree with Patrick as the star on top.
As evening sets in in both Toonvile and Halloween Town, the Mayor argues with Jack that his Christmas takeover plan is not a good idea. To this, Jack promptly kicks him out of his house, telling him to go find a job in Christmas Land. The Mayor does so, but not before he says he is being an ass. After the Mayor has left, he says "there's got to be a better way to take over Christmas." Just then, he picks up a book called "The Olden Guide to Conquering Christmas". In it, he finds a ritual to summon some help to take over Christmas. In the ritual, he crushes a lemon and pours it into a beaker that emits red smoke. He then is taken to the home of a strange Bugs Bunny-esque creature. Jack promptly asks the creature to help him conquer Christmas, and he agrees. Saying " IT WILL BE "
Back in Toonvile, Bloo prepares to send the final letter to the North Pole using the launcher, but stops when he realizes Patrick hasn't finished his letter yet. King Pig, meanwhile, has his dream rudely interrupted by Bloo intrusion while he is sleeping. Bloo, who believes Santa Claus, decides to write a letter to him.
When the partygoers outside try to get Bendy to come out of the house, due to them planning to prank him, he summons a big phone from the sky to silence them.
Just then, a large red car crashes through the squid's bedroom. When the driver reveals himself, it is revealed to be Santa, for whom the partygoers have been waiting for. This Santa, however, is actually Jack wearing a paper Santa mask. The real Santa Claus has been trapped in a painting. Once revealed, Jack springs his trap, transforming the Santa painting into one of the mysterious creatures from before. The painting then sucks up The Gang a la the final boss battle of Luigi's Mansion.
"It's a Foster Christmas? ACT 2"
The group wake up to find themselves in another dimension, which is an area surrounded by an impassable wall, consisting of a gigantic Christmas tree with a spire and a pentagram star at the top, a large igloo, and a gingerbread village covered by a large storm cloud. Jack suddenly reappears at the base of the tree holding the book, where he starts reading out a summoning chant. The chant summons a gigantic monster with the lower half of a spider styled furnace and the top half of a mangled bugs bunny with devilish eyes. The beast is the Black Hiver, a sadistic holiday demon As the Hiver spews fire, Bloo faints while Jenny, the Eds, and Patrick flee. Meanwhile, TBA stands their ground and proceed to do battle with the demon. TBA and TBA move in to attack, dealing some damage to the beast, but the TBA uses its mind controlling power to suck out their souls, killing them. TBA fires a giant log which separates TBA from TBA and TBA, they then discover that TBA and TBA were turned into robotic minions whose sole purpose is to destroy anything in their path, including imaginary friends.
Meanwhile Ed, Wilt, Edwardo Coco, Patrick and Jenny are still running and make their way to the igloo where they meet Patchy the Pirate who hears three bells, and asks them what three bells means. Patrick and Ed assume that it means ice cream, but then Patchy theatens to take their lives. Ed attaches the "missile-toe" to Jenny's head to help them fly away; but while celebrating they are knocked out of the air by floating boulders, which results in Patrick falling to his death and being eaten by Patchy. Ed and Jenny survive the fall but the Hiver uses its mind controlling powers again to suck out Jenny soul and turns her into an icy ghost like robot with chainsaws, who beheads Patchy and chases Ed, Wilt, Edwardo and Coco out of the igloo.
Meanwhile in the gingerbread village, Stan, Kyle, Kenny and Cartman Double-D and Eddy wander though the village streets, where they find out that there are zombie gingerbread men after them. They run for the exit of the village where they are stopped by a large demon nutcracker. Several zombies are shot down by TBA who eventually runs out of bullets, the three are then greeted by the Hiver who breathes fire on the trio, killing them; afterwards they are picked up and eaten.
On top of the tree, Jack exclaims that "THIS YEAR, CHRISTMAS WILL BE OURS". Santa, still trapped in his painting, warns Jack that the Hiver cannot be trusted, and that should he succeed, he would never get his holiday back. Jack, however doesn't believe him, saying that the book doesn't say so and that he's only taking over Christmas for this year. Soon Jack realises that its almost midnight, which means that he has almost won.
Bob and Larry epilogue
The 2D animation of the show was done in-house by The Bloo, as well as by Saerom from Korea and Bardel Entertainment in Canada. In addition to that, the CGI animation was done by Mainframe Entertainment and the stop-motion animation was done by Aardman Alternative and Cuppa Coffee Studios.