Barf and Belch were one of the captured dragons used to train the Viking teens. The lesson they taught was to work together to find the head that lit up the gas (which was Belch). Later, Hiccup manages to get Ruffnut and Tuffnut to bond with them in time to help defeat the Red Death.
At the climax of the film, Ruffnut and Tuffnut, along with the rest of the Viking's teens, were on dragons. They helped the twins distract the Red Death to allow Snotlout and Fishlegs to attack them. By the end of the movie, the twins are seen riding Barf and Belch along with the other Viking teens.
In the movie "Gift of the Night Fury" when Stoick is having a little speech about spending Snoggletog with the dragons. A particular roar interupts them, as the dragons start to stare up to the sky spotting a flock of other dragons. A Monstrous Nightmare climbs on top of a roof and roars which makes all dragons take off and follow the flock of dragons.
There is a brief shot of Barf and Belch behind Ruffnut and Tuffnut. looking up to the sky to spot the flock heading off to an island called the "Rookery" to have eggs.
Although it is not shown that Barf and Belch fly off with the other dragons, or even shown on the island itself, they are later to be found when the dragons land back on Berk with an abandoned viking ship transporting all of the dragon babies.
They are seen landing in the background, behind Hookfang and Hiccup.
It was revealed in the show that the left head's name is Barf and the right is Belch, with Ruffnut commanding Barf while Tuffnut controls Belch.
Barf and Belch inadvertently get knocked out by their own Riders in "Viking for Hire" when they try out a new saddle that Gobber made. The saddles have built in catapults, which when used, fling rocks right into the dragon's heads.
In, "In Dragons We Trust", Barf and Belch were framed by Mildew of the crime of stealing all the boots of the village during Boot Night. Zippleback tracks lead to Barf and Belch, sleeping in a pile of the village's boots. Hiccup discovers later that the tracks were made by a pair of Zippleback Boots Mildew had. Based on this percieved crime and others, Stoick banishes all the dragons to Dragon Island.
When the village is attacked in "Alvin and the Outcasts", the dragons are retrieved from Dragon Island and save the day.
In "Twinsanity", Barf and Belch briefly went rogue after Ruffnut and Tuffnut's conflict with each other reached a point where they were issuing contradictory orders to the head they controlled. The Zippleback was roaming around the village just as renegade Viking chief Dagur the Deranged arrived to discuss a treaty. Wishing to sign the treaty in dragon's blood, Dagur captured and nearly decapitated Barf and Belch, but the twins were able to reconcile in time to help their dragon escape, with the other dragons faking an attack on the training ring to conceal Berk's newly trained dragons in order to avoid provoking war.
Barf and Belch appear in almost every episode, appearing alongside or being ridden by the twins.
in "Zippleback Down", they accompany the twins as they attempt to dislodge hidden traps. When Tuffnut is captured, they are ordered by Ruffnut to watch over her brother while she attempts to go get Hiccup so he can free her brother. Although annoyed by Tuffnut's constant efforts to start a conversation with them, they end up playing with him (though Tuffnut didn't enjoy it much). They try to protect Tuffnut when a wild Typhoomerang (Torch) aggressively approaches him. Defending Tuffnut, they are caught in a bola-string trap, but they manage to cause a big enough explosion to start a forest fire somewhere off. They are freed by Hiccup when he arrives on Toothless and they ride Torch. The Zippleback end up helping to put out the forest fire and arrive back home on Berk safely on Torch's back. Later that night, when Ruffnut fails to free her brother from the trap and ends up with both of them being trapped, they leave their riders to bicker to presumably return home.
in "A View to a Skrill, Part 1", Barf and Belch help to free the Skrill from the ice block, along with Snotlout and Hookfang. The twins ride them and they help to snuff out the Skrill from the clouds so Hiccup can knock it down. They manage to save Hiccup from being blasted by lightning, although the twins and them end up being chased themselves. Barf and Belch manage to land safely on an outcropping of land in the middle of the ocean and help the twins go after Alvin when they see him collecting the Skrill. In "A View to a Skrill, Part 2", they are seen on Outcast Island being watched over by Ruffnut as Tuffnut and Hiccup try to gather information about the Outcast/Berserker alliance. They appear again later to help Toothless seal up the hole, trapping the Skrill in ice once again.
In "Cast Out, Part 2", they were seen in the end to both agreed together to separate their riders from fighting each other.
Barf and Belch then helped the other dragons and their riders in catching Silent Sven's sheep. They took part in the first two dragons and the official first one in which their riders cheated.
in "Dragon Eye of the Beholder, Part 1", along with their riders, Barf and Belch assisted Ruff and Tuff in worshiping Loki. During one of their pranks, they found Trader Johann. They then went with the other dragons and their riders to find Dagur at the Ship Graveyard. However, they were then scared off by the eels. However, they then returned to rescue Ruff and Tuff before they fell. In "Dragon Eye of the Beholder, Part 2", they helped their riders in obtaining a Snow Wraith tooth.
Barf and Belch briefly appear being ridden by their riders, Ruffnut and Tuffnut. Barf in particular shows annoyance and slight aggressiveness when Snotlout approaches Ruffnut to flirt with her. Later on, they were also seen to be very upset about Stoick's death before being controlled by Drago's Bewilderbeast. Like all the dragons, Barf and Belch broke free from the Bewilderbeast's control, and acknowledged Toothless as their new Alpha. They then rejoin back to their owners, with both heads trying to comfort Ruffnut. Belch was rejected by Ruffnut, but Tuffnut quickly grabbed his head to be happy to rejoin together.
Barf and Belch go to Nepenthe along with the twins. While traveling there, they are accompanied by Tidal Class dragons that bring tribute to their new alpha. Barf and Belch then let the twins ride a pair of Seashockers, but are upset by this. Later, when the twins mount them, they give them an angry look for riding another dragon.
On the island, Barf and Belch relax in a hot pool along with Toothless, Hookfang and Meatlug, instead of focusing at the task. At dinner, they, along the other dragons, began devouring the food. They then collapse and the riders are captured by Calder and his men.
After Hiccup escapes, he brings the other dragons, including Barf and Belch. The riders prepare to leave, but right then some Foreverwings wake up and began destroying the village. Barf and Belch help by getting the people to safety. After Hiccup defeats Calder, Barf and Belch arrive at the scene to see what happened.
The next day, Barf and Belch are seen head-butting each other, just as the twins do.
Barf and Balch are caught up in a net of webbing produced by frenzied dragons called Silkspanners, they are rescued by the Dragon Riders and fight back. Later, the Barf and Belch travel with Hiccup, Eret, Gobber, and Astrid Hofferson and their respective dragons to find the source of the dragonvine plant. The scent takes them to Dragonvine Island and find a village of people in trouble. The Riders and their dragons burn away some of the encroaching dragonvine. The group splits up again, this time the Barf and Belch with the Twins and Eret search out the source of the dragonvine on the island, while Hiccup, Astrid, and Gobber look for the Silkspanners. One of the villagers - Bayana - accompanies them. The group finds out that the villagers have been growing and harvesting dragonvine to protect themselves from people like Drago Bludvist. The villagers capture the group - both Riders and dragons - and toss them into a pit full of dragonvine in order to preserve their defenses and village. In the meantime, Hiccup's group finds the Silkspanners and brings them back to Dragonvine Island as it turns out they are able to eat it. Barf and Belch's group is saved.
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When Toothless and the Light fury were captured by Grimmel. Barf & Belch along with all the other dragons came to alpha's help. But Toothles ordered them to stop when Grimmel threatened to kill the Light fury.