The Unstoppable Yellow Yeti

Leaving from a summery island, Osmo and his dad Nick are going to a town called Winterton to meet his cousin Rita. As they arrive, Mayor Chrome tours them while thinking that monsters aren't real. However, Osmo notices that his surf board is missing and tries finding it. He only finds half of the board with some big foot steps. Following them, he finds an area with someone in it and gives him the other half. Coming out of the area is a giant yellow yeti named Gustav, which Osmo gets freaked out by at first, but noticed it speaking. Gustav confirms that there is other monsters in the town but he isn't allowed per the rules. Rita takes a peak noticing that monsters exist, so she gets an old man to sound the alarm, scaring Gustav, though Mayor still doesn't believe that monsters are real. The people of town start singing which scares Gustav more, so Osmo makes earmuffs for him. Thanks to Osmo yelling at Gustav, an avalanche starts to fall down. As Osmo rides on Gustav, Rita notices that she will get run over by them.

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Continuing the plot from the previous episode, Gustav flips positions and Rita starts riding on him. Landing to Rita's house, her parents arrive and tells them about a monster inside. Osmo and Gustav get worried, since Rita's parents think about killing the monster if they found one. Osmo and Rita want save Gustav so that he is not in danger. Rita tries distracting her mother while Osmo sneaks Gustav to get out of the house, which turned out successful with Gustav in a bag of clothes. With dinner ready, everyone hated the meatballs. Gustav comes in disguised as a chef named "Chef Yummy Sasason", with the meal being "comfort food", food that comes out of Gustav's feet as seen earlier in the episode. Everyone liked the food except for Osmo and Rita, and Mayor welcomes Osmo and Nick to the town. As Gustav originally wanted to go back to the mountain, Osmo wanted him to stay with him as he thinks he belongs here.

Everyone in Winterton has a ski armlet except for Osmo, as per the rules of the town that everyone should have ski armlets, Osmo has to earn one or else he is banished. Gustav starts to teach Osmo on how to ski, though his skiing is different from human skiing. Gustav gets Rita to teach Osmo on how to ski, though it all doesn't work out as he keeps bumping into trees. As Mayor reports to Osmo about his exam, smashing into a tree counts as an aromatic failure. Now he has to pass by challenge, with the race course being one of the tallest mountains. Gustav distracts Mayor by eating an ice cream cone with sprinkles which violates the rules, and gets Osmo to finally pass the Mayor. With the Mayor winning, he violates one of the rules by swallowing the ice cream and pushes Osmo. Osmo wins the race and gets his armlet.

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Watching a horror movie titled The Yoel of the Yeti, Gustav gets offended because he hasn't seen any yeti act like they would always just scare, which is why the Yeti species gets a bad reputation because of the stereotypes of them being monsters. Everyone got scared because they watched the movie. Later in the morning, Mayor once again clarifies that monsters don't exist. Mayor decides to do a practice drill if a monster came to town. Gustav comes in disguised as "Frank McDanielson" to play the "most realistic" portrayal of a yeti. In the yeti suit, he plays around giving people hugs, make snow angels, build snowman, riding a baby and juggling. Gustav announces that yetis aren't monsters as many would think. The baby grabs Mayor's legs, and the baby cries because of Mayor being mean to him. This triggers Gustav, as he would save the baby from more harm. Almost everyone however start freaking out. Gustav pushes a tree which the Mayor runs into. As he can't tell where he is going, he is on a plate of ice in the river, which would flow into bears, a saw mill and a water fall. Gustav rips his costume off and saves Mayor. Mayor didn't see Gustav to prove that yetis are sometimes heroic however, though the baby isn't scared of him. The Mayor announced a competition with a trophy, with himself being the winner, though Gustav would secretly steal it from him while announcing a celebration.

Going to Winterton peak, the gang, alongside Nick and Rita's parents are on a camping trip. Osmo learns about the founders of the town, Sir Wallace Wint and Emma Ertton. Rita goes to the mountain to find where Ertton camps at. Anders starts following the trio to see what they are finding. They did lose the map, but Gustav senses a smell of the fish fins and finds it, which gives Rita excitement, and found where Ertton was camping. Gustav wants to badly but Rita wants it intact for historical purposes. The gang found a snow fort with Anders and his friends. They steal the fish fins and the gang tries getting it back, only for them to lose it. Only happens however that Anders has the fish fins already. He opens the can and smells the stink, which would later get into the camp of the parents of Osmo and Rita.

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After losing a game of Combocky, the gang goes to a pity party which in itself is a spa. After Rita scared them in a mud monster disguise, Osmo and Gustav bump into ice and notice red steam. The gang got away from the while Gustav holds his breath, as breathing in the steam can turn him "full monster", and thinks that humans won't get the syndrome if they breathe in the steam. Gustav is tied in rope upside down so he couldn't escape and pass out. Osmo and Rita both find possible weaknesses for the syndrome. Later in the morning, it turns out that Gustav is actually fine and doesn't have the syndrome. Rita starts acting funny however, going in rage for a bit. Checking on her, she noticeably has red eyes and howls like a wolf, having the "full monster" syndrome. Gustav gets excited but Rita isn't doing this purposely. Gustav questions if humans are half monster, so Osmo tries finding a cure, only for him to get the syndrome as well. Gustav is freaked out thinking that he is gonna get eaten, so he looks into a book about the syndrome and finds out the cure is skunk cabbages. Chasing them to give the cure, he shoots the cabbages with the hockey stick thrown directly to their mouths. Osmo and Rita are now back to normal.

As Mayor got himself a new rug, Gustav thinks that the rug was the skin of his grandpa, and cries about it. Osmo, Rita and Gustav decide to take the rug to the monster mountain graveyard with a traditional yeti funeral. However, after an owl steals the rug, Gustav catches it while falling on branches, them resulting in the rug to rip. A little of the rug still remains however. While barring the remains, turns out however that that Gustav's grandpa is still alive and comes to graveyard to spend time with his dead friends. It also turns out that the rug was actually manufactured. Gustav's grandpa now uses the rug remains as a wig.

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Osmo wants to see if his inflatable donut has returned to him, but sees nothing in the mailbox, waiting for a whole month after leaving it behind. The gang tries to find out what happened to Winterton's Mail Cats. Gustav finds a hat of Mr. Pufflelum, getting Osmo and Rita excitement. The gang finds the packages including the donut, along with the cats, who all have gone feral. The cats trap the gang inside a litter box, so they summon the Northern Lights for help. The lights take the donut and eats it, then uses laser beams to distract the cats so the gang could get out. Gustav breaks the cage with his cat allergies and gets the packages, with everyone finally getting their deliveries.

While fishing after Gustav breaks the ice on the lake, Osmo catches a sea monster named Octavia, which jumpscares Osmo and Rita. The roaring however was monster for "hello". When Octavia is outside for too long, she drys so she gets back in the water and gives the gang lots of fish. Octavia later pops out of the sink, so the gang distracts Rita's mother. The gang and Octavia would later go outside for fun. Gustav sprays Octavia whenever she gets dry. Later the gang is back inside, where Octavia would eat the humans. Gustav warns the kids about it per sign language. Gustav pretends to cook the kids as "children chilly". As Octavia gets dried-up, Gustav reveals that this is actually a trap by him and Octavia escapes in the sink with Gustav blowing her.

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In a school, Gustav is disguised as a kid named "Rod Rego". The class watches a video where in 1917, monsters kicked barrels of pinesap, resulting in a flood of pinesap. The town sticks themselves together to save themselves, which works they the flood resulted in a new holiday. After the video was over, the gang goes to festival that celebrates the day. The people of the town would sing a song which scares Gustav, though Osmo does interrupt the singing. The gang would do some activities with Osmo trying to show himself as a true member of the town. Anders announces that he created a pretend flood with Mayor. Osmo and Gustav however, created a stack of 99 Pinesap barrels to create a giant real flood to an anthemic recreation of the original flood. The barrels start breaking which creates the flood. Osmo warns everyone about a real flood coming in, with the people running from the flood. This plan works and Rita congratulates Osmo for saving the town.

Gustav flushes a legendary toilet, which causes everyone in town to want to sit on it.

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A living puddle starts to imitate Osmo.

Rita must win against Anders in a sauna dance battle.

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Osmo finds a cute monster that he finds inoffensive, but later starts chewing on everything metal in town.

After a glacier that was supposed to break apart at the beginning of spring stays intact, everyone suddely falls in love with each other, much to Gustav's disgust. He starts to do some tasks for the Northern Lights in order to make the glacier break.

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After stealing a mysterious stone from her mother, Rita starts noticing her acting strange, with her most notable trait being red eyes, which makes her start believing that she is a monster. In truth, the stone was actually an old friend of hers and the red eyes were to scare Rita.

While building snowmen, Rita and Osmo both get hit by snowballs with them suspecting that one of them started it. Two more snowballs were thrown and they now suspect Gustav as the thrower. Both started throwing snowballs at him and loses his sandwich. The trio is now dueling with each other, and started the fight when Gustav roared. They are started getting tired however, but it actually an anthropomorphic tree that was making the trio have the argument.

The gang is having their picnic when all of a sudden, a weasel shows up stealing their food. They must catch it before it eats all of their food. The weasel would later get stuck in a tree with Gustav catching it, but unfortunately, more weasels appear eating their food.