Shiny Magikarp Raid is Available for a limited time.

If you login to Pokemon Sword and Shield, in the Wild Area from now to January 3, any promoted raid den with a Magikarp in it will have a 2/15 or 13% chance to get a Shiny Magikarp.

In order to have Magikarp appear, all you have to do is go to the Mystery Gift tab and then click “Get Wild Area News”.

After that, throw Wishing Pieces in raid dens and eventually, a Magikarp will show up. After enough tries, you should finally encounter a shiny one.