It sounds like you might be thinking of Magikarp, a very common Water-type Pokémon known for its weak stats and its evolution into the powerful Gyarados.
To find a shiny Magikarp, you'll need to play a Pokémon game where it appears:
* In the wild: This is the most common way to find shiny Pokémon. You'll need to encounter many Magikarp and hope that one of them is shiny. Shiny rates are generally low, but some games and events have increased shiny rates.
* From eggs: In some games, you can hatch Magikarp from eggs. The shiny chance is the same as for wild encounters.
* Specific events: Some games have events where shiny Pokémon appear more frequently, such as the "Shiny Magikarp Event" in Pokémon Go.
* Trading: You can trade with other players to try and get a shiny Magikarp.
Remember, finding a shiny Pokémon is all about chance and luck! Good luck on your hunt!