Casey equipped Chikorita with a band on its head. She had Chikorita battle a Rattata, who got tackled by Chikorita. By using a Poké Ball, Casey caught Rattata and called Chikorita in its Poké Ball. After challenging Ash, Casey sent Chikorita, who used Vine Whip to bind Charizard by its neck. However, Charizard retaliated with Flamethrower, burning Chikorita's leaf and making defeating it. Casey was enraged and challenged Ash to a rematch later on. Chikorita used Sweet Scent, which affected Ash's Pikachu, then tackled him. Pikachu retaliated with Thunderbolt, but Chikorita spinned its leaf to repel the attack, then tackled him once more. During the middle of the battle, Team Rocket snatched Pikachu and Chikorita. Fortunately, Casey had her Pidgey and Rattata take back both Pokémon. Chikorita used Razor Leaf and Pikachu used Thunderbolt on Team Rocket before blasting them off with Tackle.
Finding a lone Chikorita, Ash recalled Casey, whose Chikorita battled a Rattata she eventually caught.
Casey met the heroes at the Bug Catching Contest, where they noted how Chikorita grew stronger. During the Contest, Chikorita used Razor Leaf on one of the Weedle, allowing Casey to catch it with a Park Ball. As Casey was searching for more bugs, she had Chikorita tackle a tree, causing a Pineco to fall down. Chikorita tackled Pineco and hit it with Razor Leaf, while Casey captured it. Encountering a Scyther, Chikorita used Razor Leaf, but Scyther deflected the attack and hit Chikorita with its blades. Chikorita managed to go on its head and blind it with its own paws. Ash tried warning Casey her Chikorita was exhausted; Casey ignored him, but Chikorita got bashed on a tree. Instead, Ash and Pikachu provoked Scyther, causing it to go after them, while Casey had to find Chikorita. Eventually, Casey found Chikorita and scolded it for quitting the tournament. Misty pointed out Casey should think of her Pokémon, rather than winning the contest. Casey saw the truth and apologized to Chikorita, who returned to her. Seeing Ash and Pikachu got captured by Team Rocket, who released a missile to trap the twerps, Chikorita used Razor Leaf. Despite its fail, Casey pointed out she supports Chikorita and is with it the whole time. This motivated Chikorita to evolve into a Bayleef.
Using Razor Leaf, Bayleef destroyed Team Rocket's missile and freed Ash and Pikachu. After the contest was over, even if she did not win the prize, Casey felt she was still a winner with Bayleef on her side.
Casey encountered the heroes, who were going to Mt. Silver and showed them the Meganium, who evolved from Bayleef. Just as they found Team Rocket's balloon, Meganium launched Razor Leaf, which cut the net and caused it to fall down. Later on, James had his Weepinbell use Sweet Scent, which attracted many Pokémon. The heroes fell in a hole made by Team Rocket, but Meganium pulled them out quickly with Vine Whip. Jessie sent Arbok, who evaded Meganium's Razor Leaf and Headbutts it. Once Jessie dropped her net, due to James' Victreebel, who evolved from Weepinbell, chewing on her, Elekid and Larvitar were freed. Arbok tried to retrieve them, but got hit by Meganium's Razor Leaf. To finish it off, Meganium launched Solar Beam, which blasted Team Rocket away. After the battle, Casey had Meganium battle Elekid, as she wanted to catch it. Elekid emitted electricity to hit Meganium, but missed. Meganium retaliated with Razor Leaf, which was countered by Elekid's Thunder Punch. Meganium tackled Elekid and hit it with Solar Beam, allowing Casey to catch it. Casey was glad and promised to win more badges with Elekid.
Casey and Meganium went to a stadium in Cerulean City, but could not buy the tickets to watch the Electabuzz team playing baseball. Later on, Meganium sent to assist Misty and Georgio in battling Team Rocket. Meganium dodged Mightyena's Tackle and retaliated with Razor Leaf. Mightyena managed to damage it with Iron Tail before getting hit by its Body Slam attack. With Solar Beam, Meganium blasted Butch, Cassidy and their Pokémon away. Meganium was also used to stop Corey's rampaging Charizard. Later on, Elekid, Meganium and Beedrill were sent out to search for Corey and Charizard, who did not come back after their training.