A Nintendo RPG series that consists of 3 games, only 1 of which was officially exported from Japan, and at the time, it really wasn't a hit. The power of the Internet--and the inclusion of Earthbound 's main character, Ness, in the Smash Bros. series that otherwise stars only Nintendo characters almost everyone already heard of--turned the series' recognition and following around. If you're not familiar with Earthbound/Mother already, imagine a Final Fantasy game where all the characters, objects, and places were out of slightly cheesy but usually classy American-made '90s movies, and magic powers are replaced by psychic powers, since that's a bit more believable in the setting. Stars a baseball-playing 10-to-13-year-old kid born with psychic powers, a prettily-dressed-up girl with the same, a boy genius with a regular-sized head, and a kid prodigy martial artist who also has psychic powers. They travel the half-nonsensical and half-creepily, eerily dead-serious world of 199X seeking to thwart an alien invasion.
You make fun of Ness in Smash Bros. until you play his game.
Before and after Earthbound are Mother and Mother 3--"Earthbound" is actually Mother 2, with a non-numbered name since it was the first to appear in the U.S. it parodied. The main character of Mother 3, Lucas, who for all intents and purposes other than characterization is a blond version of Ness with a twin brother and dead mother, showed up in the 3rd Smash Bros., which of course was the tipping point for people who were kinda sorta maybe curious about Ness's series.