Expelled from the Pokémon Institute for unethical experiments demonstrating zero respect for Pokémon as living beings, Dr. Yung, known as the Mirage Master, channeled his bitterness into a quest for revenge against the scientific community. He dedicated years to developing the Mirage System, technology generating holographic Pokémon from data. These creations could materialize extinct or rare species and wield any attack, surpassing organic Pokémon in his view.

Dr. Yung operated under dual identities: publicly as a polite scientist inviting trainers like Ash Ketchum and Professor Oak to demonstrate his system, and secretly as the masked Mirage Master in a black cowboy hat, cape, and metal mask. He used a holographic projection of this masked persona during his initial appearance to fake the kidnapping of his public identity, obscuring his true role. He regarded all life as expendable, repeatedly dismissing the sentient Mirage Mew as a "flawed specimen" due to its independent will and emotions.

His plan involved kidnapping Professor Oak and torturing Pikachu to extract memory data, forcing Oak to reveal his laboratory password "REDGREEN." This granted access to global Pokémon databases, enabling the creation of Mirage Mewtwo—a composite entity designed to assimilate all Pokémon data and possess no weaknesses. To power it, he uploaded the entire Mirage System's data, including Mirage Mew. Mirage Mew retained consciousness within the merged data stream and resisted assimilation. This interference immobilized Mirage Mewtwo during its final attack, allowing Pikachu to destroy the system.

Facing defeat, Dr. Yung rejected surrender and walked into his collapsing, burning laboratory. His body was never recovered, leaving his ultimate fate uncertain.