Mark

Mark is a minor character that first appears in Pokémon J. He only appears in Pokémon J and does not appear in Pokémon M.

Description
'Mark looks and seems like an ordinary trainer, but he got some powerful tricks up his sleeve. He uses the power of Normal-Type Pokémon and is a Gym Leader who uses them. His younger sibling is Jason, who tries to compete with his older brothers.'

Pokémon
Mark uses a Mew, since it can learn Normal-type moves, which includes Transform.