With Mr. Stone
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 Forecast Ability 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 taken a liking to the boy.
In Mind-Boggling with Medicham, Fofo advanced Ruby through the Normal Rank of the Smart Contest. In Going to Eleven with Loudred & Exploud I, Fofo is used alongside Ruby's other Pokémon to battle against Courtney and her Ninetales. Although Ruby had a five to one advantage his team was beaten due to Ninetales having control of nine different fireballs.
In I More Than Like You, Luvdisc I, Fofo advanced Ruby through the Super Rank of the Smart Contest. After the contest Fofo is used in Ruby's battle against Wallace alongside the rest of his team, bar Feefee, and loses.
In Always Keep Whiscash on You for Emergencies, Fofo advanced Ruby through the Hyper Rank of the Smart Contest.
In The Beginning of the End with Kyogre & Groudon X, Fofo, alongside Ruby and Sapphire's other Pokémon, battled Archie and Maxie. Fofo was seen using Hail off of Walrein's Icy Wind. Being in her Snowy Form, Fofo used a powerful Weather Ball to defeat Archie and Maxie.
In It All Ends Now VIII, Fofo battled alongside the rest of Ruby and Sapphire's Pokémon against Maxie and Archie. Later that day, Fofo is shown to have won the Master Rank of the Smart Contest, wearing a Green Scarf.
In A Cheeky Charizard Change-Up I, Fofo was seen cheering Emerald on during his battle against Tucker.
In Omega Alpha Adventure 2, Fofo battled a wild Claydol inside the Sky Pillar. She quickly defeated it with Hail.
In Omega Alpha Adventure 15, Fofo used Sunny Day to blind Rayquaza, allowing Ruby and Norman to get close to it.