Starmie is available in Pokemon Sword and Shield's first DLC pack the Isle of Armor.
Turning a Staryu into a Starmie is pretty simple, here's how!
Water Stone
To turn a Staryu into a Starmie it must be exposed to a Water Stone.
Water Stones can be found in the main game, hidden on Route 2, in Bridge Field or Lake of Outrage in the Wild Area.
