Regice was Brandon's fourth and final Pokémon against Ash, battling his Pikachu. Pikachu fires Thunderbolt, which does no damage. Regice uses Blizzard, which blows Pikachu away. Pikachu attacks with Iron Tail and Quick Attack, but Regice negates it with Ice Beam, which freezes the field. With the field covered in ice, Regice can move quicker, but Pikachu ends up slipping. Regice attempts to use Focus Punch, but Pikachu uses Thunderbolt to paralyze Regice, and then strikes the Iceberg Pokémon with Iron Tail. Regice uses Ice Beam to freeze the stadium more, creating a tomb of ice pillars that trap Pikachu.
With Pikachu immobilized, Regice uses Rest. Pikachu uses Iron Tail to free itself. Pikachu races towards Regice, but it wakes up and fires Ice Beam, this time making a direct hit and freezing Pikachu in an ice pillar. Ash orders Thunderbolt, but Pikachu seems unable to. The referee begins to declare Pikachu unable to battle, but Pikachu uses Thunderbolt to shatter the ice. Regice fires another Focus Punch to send Pikachu bouncing across the ice field. Ash manages to get Pikachu to use two Iron Tails in the row due to the ice. Regice uses Ice Beam to trap Pikachu in another icy tomb before using Rest again. Pikachu frees itself with Iron Tail and starts charging forward with Volt Tackle. Regice wakes up and uses Ice Beam to try to freeze it again, but Pikachu dodges and hits Regice before it can launch another attack, knocking it out and earning Ash the Brave Symbol.
Regice was also used to battle Regigigas, but was confused by the Colossal Pokémon's Confuse Ray and went on a rampage along with Regirock and Registeel. When the evil Pokémon Hunter J attempted to capture Regigigas, Regice, Regirock, Registeel and Brandon were all turned to stone in order to protect it. After J left due to her client cancelling the deal, the Regi's and Brandon were revived by Regigigas and stayed at Snowpoint Temple in order to rebuild it and guard Regigigas.