Misty's Psyduck is a pokémon caught by Misty in Kanto.
Psyduck was the fifth Pokémon she caught. It is still with her in the Cerulean Gym. Psyduck is almost useless, except for his Psychic Attack. Psyduck almost constantly escapes it's Poké Ball during every battle that Misty is in.
She caught it by accidentally dropping her Poké Ball and Psyduck touching the button. Although it can sometimes annoy Misty, she and Psyduck have a good bond and Misty refused to trade it for any Pokémon no matter what.
It was close to evolving and Misty thought to have evolved into a Golduck during the journey through Orange Islands, but it was later revealed to be a wild Golduck that liked to impress girls.