Milotic was a formidable opponent in battle and was also an expert in contests. It was described by Juan as being his "dear old friend", as they had spent many years together.
Milotic put on a show with all of Juan's Water type Pokémon. It was also used to defeat Team Rocket by breaking out of their electric net with Iron Tail and then sending them blasting off with Twister.
Milotic was the last Pokémon Juan used in his battle with Ash. Swellow dodged Milotic's Hydro Pump and hit it with Aerial Ace. Milotic tried retaliating with Iron Tail, but Swellow used Double Team and evaded the attack. Instead, Milotic fired Twister, which defeated Swellow. Ash sent out his last Pokémon, Pikachu. Pikachu fired Thunder, which effectively wounded Milotic. However, Milotic used Recover and healed itself. Milotic used Iron Tail and clashed with Pikachu's Iron Tail, but it bashed the latter away. Milotic placed its tail in the water and fired Twister, which hit Pikachu away, but the latter used Thunder and stopped the attack. He then attacked Milotic with Quick Attack, so the latter used Hydro Pump. Pikachu avoided the attack and fired Thunderbolt, which electrocuted Milotic, who healed itself once more with Recover. Milotic dived in and came closer to Pikachu to attack it with Iron Tail, but failed. Instead, Pikachu jumped onto Milotic, evading its Hydro Pump, then flipped it into the water. Pikachu dived in as well and launched a powerful Thunder, which effectively defeated Milotic.
Before arriving to Slateport City for May's Grand Festival, she and Ash remembered their past adventures so far. Ash recalled facing Juan, whose Milotic fired Twister to defeat Ash's Swellow. Pikachu was sent out, though he had trouble facing Milotic underwater. Pikachu charged towards Milotic, evading its Iron Tail and Hydro Pump attacks. Then, Pikachu tossed Milotic underwater, where he defeated Milotic with Thunder.