Human Snowball

Some guy is skiing or snowboarding. Suddenly he trips and starts tumbling down the slope, as he tumbles, snow gathers up around him until he's now seen as a giant snowball rolling down the hill.

See also Gravity Is a Harsh Seamstress.

Anime and Manga

 * Used as an inventive way to get rid of a body in a Detective Conan case.
 * Happened to Tubby in an episode of the Little Lulu anime.
 * In one episode of Pokémon,  are victims as they were

Comic Books

 * A lethal version occurs in the Tintin story Prisoners of the Sun in which Captain Haddock becomes a snowball and causes the same to happen to some unfortunate Mooks in the Andes. Cliff ensues, only the captain survives thanks to a rock in his way.

Commercials

 * A commercial for Doctors Without Borders used a rolling ball of people as a metaphor for the spread of AIDS. Travelers Insurance did a similar spot soon after Citi spun it off, using a ball of people as a metaphor for risk. Critics compared both to Katamari Damacy.
 * Some smartass went and added the Katamari music to it. It's hilarious.
 * Because Katamari Damacy can't get enough Shout-Out, there's a Traveler's Insurence commercial with this. And a normal one.

Film -- Animated

 * Happens to Scrat in Ice Age.
 * A scene from Kung Fu Panda 2 showed Po and the Furious Five traveling up a large snow-covered mountain. While they make their way down the other side, Po trips and starts rolling down the mountain as a whole bunch of snow gets built up around his body.

Film -- Live Action

 * The movie Willow has a live-action version of this.

Literature

 * At the start of Christmas Catastrophe, Geronimo Stilton gets into one with another mouse, then they both hit a rock. Life sucks.

Live-Action TV

 * Thunderbirds, normally rather serious, has this happen to Parker fighting an assassin, rolling down a hill in "The Cham-Cham".

Video Games

 * Happens in Super Mario World 2: Yoshi's Island if you hit a rock during one of the skiing sequences.
 * One of the powers in the Wario Land series is exactly this (Snowman Wario). And he turns into a giant snowball seemingly INSTANTLY after standing on any form of slope or slanted ground (and can break certain blocks).
 * In Wii Fit, jumping too late during the ski jump minigame causes your Mii character to miss the jump and turn into a giant snowball.
 * Katamari Damacy is this trope applied with everyone. We ♥ Katamari even has an actual level where a giant snowball was the goal.
 * Losing in a Bionicle minigame.
 * It's one of the powers in Kirby 64 achieved by combining 2 ice powers.

Western Animation

 * Buzzsaw Louis in Veggie Tales: The Toy That Saved Christmas.
 * Happens with a huge wad of gum in Chowder, with the sticky gum and music culminating into a huge Katamari Damacy Shout-Out.
 * Happens to Bullwinkle in one of the opening segments on Rocky and Bullwinkle.
 * Happens Katamari-style in the Ed, Edd 'n' Eddy episode "May I Have This Ed?", where a bunch of kids get stuck to Rolf's blow-fish costume.
 * In one of Chuck Jones' early "Two Curious Pups" cartoons, one of the dogs falls down a snowy hill, but instead of a ball, the snow accumulates in the shape a giant dog.
 * Played with in the Looney Tunes short "Daffy and Tom Turkey". Porky chases Daffy down a series of hills, with Daffy forming a snowball as he runs down the hill, then shrinking back to Daffy as it rolls up the next hill. Eventually, the snowball shrinks down to nothing, confounding Porky. Daffy, of course, is just offscreen, ready to pelt Porky with a snowball.
 * Happens to Betty Boop in her incomprehensively strange adaptation of Snow White.
 * Happens to Jerry of Tom and Jerry in the opening of Snowbody Loves Me.
 * Happens to Bart and Homer in one episode of The Simpsons.
 * Happens in the My Little Pony Friendship Is Magic episode "Winter Wrap-Up", after Twilight's attempts to use her magic to help clear the snow goes awry.
 * Happens to Amos the mouse in the Miscellaneous Disney Short Ben and Me just right after being frightened by a cat (resembling Lucifer from Cinderella) peeking through a window on his way toward Benjamin Franklin's house.
 * On Jimmy Two-Shoes, Molotov actually does this to one of his own men as a battle tactic.
 * Happens to Socrates and Aristotle in an episode of Adventures from the Book of Virtues.
 * Rudolphs Shiny New Year does this and makes 3 human and one reindeer snowball.