Dewgong

Dewgong is the final stage of evolution for Seel. It stores thermal energy in its body and can swim at a steady eight knots even in intense cold. In "The Misty Mermaid," Ash and friends return to the Cerulean City Gym to visit Misty's sisters. While visiting, Misty participates in a water ballet that gets ruined by Team Rocket. A Pokemon battle follows, and during the fight, Seel evolves into Dewgong to blast Team Rocket into defeat.

First appearance: Episode 63—"The Misty Mermaid"