Once Upon a Snowman is the untold story of how Olaf came to life and set out to find his destiny.
During Elsa's song "Let It Go", Olaf the snowman is brought to life. Before he can do anything, however, she releases her cape, which flies and knocks him down the mountain side until he crashes into a tree. Not knowing who he is, or why he is alive, he decides to find an identity for himself. He comes upon Wandering Oaken's Trading Post and Sauna (where Kristoff can audibly be heard singing "Reindeer(s) Are Better Than People" from the barn) and gets flattened by the front door by Anna, who exits not noticing him and carrying a bag of carrots (which she will eventually give to Kristoff and Sven as payment).
Olaf enters the Post and meets Oaken, who does not seem all that surprised by the appearance of a talking snowman. Olaf asks for a nose, possibly a carrot, for his face, but Oaken explains that he sold the last batch and decides to help him out by trying a variety of other objects. One of the objects is a stereoscope that features images of "summer". Olaf is immediately taken by it and wants to experience it before settling on a sausage for his nose.
As Olaf happily leaves with his new nose, a pack of wolves suddenly appear and begin to chase him through the snowy tundra, during which Anna and Kristoff can be heard arguing with each other over the concept of love. Olaf passes by them, again unnoticed, which gets the wolves to suddenly shift their attention to them. Olaf continues to slide and witnesses Anna, Kristoff, and Sven making a leap across the gorge while ditching their sleigh. Olaf makes it to the bottom, where he spots one of the carrots that gets dropped, but it gets crushed by the sleigh.
Olaf's sausage nose breaks, which saddens him. Upon seeing one of the wolves whimpering pitifully at his nose, he gives it to him, believing that he needs it more than him. The wolf happily licks and snuggles with him before leaving. Olaf comments that it felt like a warm hug, which suddenly causes him to remember Anna and Elsa's time playing together as children. Finally realizing who he is, he comments "I'm Olaf and I like warm hugs."
During the credits, Olaf is seen coming across Anna, Kristoff and Sven who will eventually give him his iconic carrot nose.
This is the first Frozen film not to feature an original song or the word Frozen in the title.
This short has a handful of inconsistencies.
Kristoff's sled exploded near Olaf, but he wasn't near the sled in the original film.
When Kristoff argues to Anna about Hans, the sled moves fast in the film, while it goes slow in the short.
In the film when Anna says "I never knew winter could be so beautiful." Olaf replies to her right by her while the short shows he isn't anywhere near her also there is no hill background.
When Olaf jumps into the air the short shows the sky is clear blue while the movie showed it's dark and Olaf is nowhere to be seen.
When Olaf lead the wolves to Anna and the others the sky isn't dark enough and when the wolves turned their attention they were going down a hill while the film shows this isn't the case also Anna, Kristoff, Sven reacted immediately rather than a seconds.
Anna's body structure resembles more of Frozen II rather than the first film.
Elsa's cape flew into the air the short shows it hit Olaf at high speed this is impossible by the short's logic.
This is the first time Anna's winter dress is shown in a short, making her the final main character to have their first film's outfit features. Elsa wore hers in Frozen Fever while Kristoff donned his in Olaf's Frozen Adventure.
Some of the images from Oaken’s stereoscope are pulled from scenes in Tangled and Moana.