Infiltration through the castle's basement waterways using Corphish and Staryu leads Ash into confrontations with Team Rocket and Mirage Pokémon sent by the Mirage Master. The battle results in Pikachu's capture, Misty thrown from a platform, and Ash briefly knocked unconscious. Upon waking, Ash discovers an injured Mirage Mew, recognizing its unique nature among artificial Pokémon. He frees it from a damaged generator, showing compassion despite its origin.

Regrouping with May (who rescued Misty) and Max outside, Ash sees the Mirage Master expand the Mirage Field beyond the mansion, deploying Mirage Legendary Pokémon. After Professor Oak deduces the Mirage Master is Dr. Yung seeking revenge, Ash joins the battle against Mirage Entei, Zapdos, and Articuno. He commands Pikachu to intercept a Flamethrower aimed at Professor Oak, leading to Pikachu's injury. Following Mirage Mew's sacrifice protecting Pikachu from Mirage Mewtwo, Ash continues opposing Yung's goal of creating imbalance through artificial Pokémon.

Throughout these events, Ash demonstrates decisive leadership in crises, prioritizes protecting both human companions and Pokémon—including artificial ones like Mirage Mew—and consistently challenges threats to the Pokémon world's natural order.