• English / United States: Master Mayonnaise
• Japanese / Japan: マヨネーズ師匠
• Japanese (Romanized) / Japan: Mayonēzu Shishō
• Japanese (TL) / Japan: Master Mayonnaise

Master Mayonnaise is a lightly eccentric old man who appears before Roy and Uruto during their Mega Evolution training in Lumiose City in the Kalos region. He allegedly spends his days searching for strong Trainers in order to popularize Mega Evolution.

He suggested that Roy and Ult train at "Mayo-maze Palace" to learn about Mega Evolution. He's also the one that gives them their Mega Rings and he introduced the duo to a mysterious Pokémon called "Yellow Blast", which ends up being Roy's Lucario after Roy battles and gets it.