Sandshrew's Locker!

Sandshrew's Locker!

Available on Prime Video, Amazon Freevee
S10 E47: A girl named Mira offers to use her Abra to teleport Ash, Dawn and Brock to Hearthome City, but after it instead takes them to a lake, Mira explains she needs their help to retrieve her submerged Sandshrew, which an ornery Gyarados fiercely guards.