Fofo originally belonged to Mr. Stone and first appeared in Lombre Larceny, having been trapped inside a fountain in Petalburg City by Team Aqua as a way to kidnap Mr. Stone. Sapphire, hearing that the Weather Pokémon was trapped, rushed in and began tearing the fountain apart to rescue her. Using her keen sense of smell she located Castform's location and had Rono chew the fountain apart. Chic then used her flames to heat Castform up. During the ensuing battle Castform used her ForecastAbility to help Sapphire figure out how to defeat Shelly's Ludicolo. After the battle Castform went with Gabby and Ty due to Mr. Stone being unconscious.
In Hanging Around With Slaking I, Castform notices Ruby and Norman on top of the Weather Institute. By knocking against the window of the car Castform gets Gabby and Ty to notice as well, and the three head over. Upon arriving Gabby convinces Castform to intervene in the father and son battle and she rushes over to use Sunny Day, stopping Mumu's Mud Shot. Though the battle has stopped, Ruby and Norman soon fall off of the staircase holding them. Due to the rain, Norman's grip begins loosening, so he asks Castform to help by shining Sunny Day to dry the pipe. After rescuing them both Gabby and Ty give Ruby a ride in their car. As they ride in the car, Castform notices Ruby's Pokémon taking care of him. Gabby tells Castform that if she wants to join Ruby, she can do so. Although Ty protests giving Ruby a Pokémon belonging to Mr. Stone, Gabby assures him that Castform has taking a liking to the boy.
Fofo is a very cautious and timid Pokémon. Though timid, she often decides to intervene in situations in order to help those she cares about. While not used often in battle, she is capable of holding her own. As Ruby's Pokémon Contest representative for the Smart category, Fofo is highly intelligent.
A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.
Ruby has a Mightyena with the name Nana and a Castform with the name Popo, both of which seem to share their names with the Ice Climbers.
Fofo's Contest call is, "Regardless of the effects of time, the smartness that this body encompasses never changes. Hopping between rain, sun, and snow with Forecast, this is the Pokémon Castform—Fofo!"