Pokemon Legends: Arceus brings together hundreds of Pokemon in a new open setting that lets you capture most monsters at will, but some especially rare ones are gated behind story progress or special quests. This is the case for the Manaphy, a mythical water-based Pokemon that debuted in Diamond and Pearl. You can get a Manaphy by completing the side quest The Sea's Legend, but this quest is anything but straightforward. Here's how to complete The Sea's Legend and claim your Manaphy.
Once you reach Coronet Highlands in the main story, you can find The Sea's Legend appear on the Request board in Professor Laventon's office. Unlike some other requests, though, this one will trigger a cutscene that tells you about the legend of a prince. It's not terribly clear what to do next from this quest, but that's because it's actually a riddle that relates to an entirely separate game.
In Pokemon Brilliant Diamond and Shining Pearl, you can find a book in the Canaleve that also describes this legend. That book references a party consisting of a Mantyke, Buizel, and a «Qwilfish with huge spikes.» So to start, you'll need to capture those three Pokemon: a Mantyke, a Buizel, and a Qwilfish.
Buizel is easy enough to find and you may already have one in your pastures, since it appears in the Obsidian Fieldlands very early. Mantyke and Qwilfish both tend to float around the Cobalt Coastlands, near the Tranquility Cove. But the legend references a «Qwilfish with huge spikes,» which means its evolved form, an Overqwil. So you'll need to not only capture a Qwilfish, but also evolve it. Or, you can wait until later in the game when it appears naturally in the world.
Unlike some Pokemon with leveling requirements, Qwilfish only evolves if you
Read more on gamespot.com