The complete Pokemon RBY pokedex, part 11

Pokémon Name: Staryu
Type: Water
Classification: Starshape Pokemon
Pokédex Number: 120
Ability: Illumiate and Natural Cure
Dream World ability: Analytic
Useful Attacks: Bubblebeam
Location Found:
D/P/P: Canalave City, Sunyshore City (fishing with Super Rod)
HG/SS: Routes 19, 34, 40, 47, Olivine City, Union Cave, Pokewalker - Beautiful Beach, Beyond the Sea
B/W: Route 13 (via Surf)

Misty uses a Staryu in the show quite often, so this Pokemon is probably doubly familiar to fans of the anime and game.

Evolution: To Starmie via Water Stone