He first appeared in Pop Goes The Sneasel where he met Ash and his friends at the summit of the Ho-Oh shrine. He overheard the shrine guard ask Ash if he would help ward off what was preventing them from getting Ho-Oh's sacred flame. Immediately Harrison offered to help too. Later hearing that it was a Sneasel that was attacking those who approached the sacred flame, he had started to make plans on catching it. Once at the top of the stairs, Harrison instructed Ash to try to get the flame while he and Misty distracted Machop and Machoke. However he underestimated Sneasel's strength and he was forced to come up with another plan.
Using Houndoom and Phanpy, Harrison and Ash took on Machop and Machoke together; their goal being to take them both out before they would get to Sneasel. Both of their Pokémon were able to hurl Machop and Machoke down the stairs leaving Sneasel by itself. After Team Rocket's brief interruption, Harrison used his Blaziken to take down Sneasel and he was able to capture it. At the end of the day, Harrison told Ash that he would meet up with him again at the Silver Conference.
Harrison's Kecleon first appeared in Can't Beat the Heat!. It was the first Pokémon Harrison sent out during his battle with Ash. It battled against Ash's Pikachu. Using its color-changing abilities and speed, Kecleon was able to hide almost perfectly, and fire some attacks at Pikachu from the tall grass, until Pikachu himself hid into the grass. Kecleon used its tongue to cut the grass, but Pikachu managed to grab Kecleon's long tongue and finish the Color Swap Pokémon with a Thunderbolt.
Harrison's Hypno was seen in Playing with Fire!, where Harrison sent it out to face off against Ash's Totodile. Totodile's Scary Face had no effect on the Psychic type, and after a stunning Hypnosis, Hypno was able to defeat the Big Jaw Pokémon with a Psychic attack. Ash next sent out Snorlax, which, however, was asleep. Harrison took the chance and had Hypno to use Dream Eater on the Sleeping Pokémon. This, however, angered Snorlax, causing it to wake up. It then defeated the Hypnosis Pokémon with a single Hyper Beam.
Harrison's Steelix was the fourth Pokémon Harrison used in his battle with Ash. It was sent out against Ash's Noctowl. After taking a hit from Noctowl's Confusion, Steelix used Sandstorm to blind the Owl Pokémon, and then hit it with Dig and Iron Tail in quick succession, knocking it out. Next Ash chose to use his Snorlax, which was quickly trapped by the Iron Snake Pokémon's Bind. However, Snorlax managed to escape Bind by using Ice Punch, and then it served the finishing blow on Steelix with a Hyper Beam.