Palkia is a Water/Dragon Type Legendary Pokemon which can be obtained with the Champion Badge (obtained by beating the Elite 4) when you obtain this badge there will be a crown next to your username, so you know that you have it. After that you must go to Elegant Valley and on the mountain area with the brown-ish grass patches (not the cave) you will look for Palkia in those patches. Palkia, like all other legendaries, can be found with a 1/1000 chance of encounter, though you can up your chances of encountering Palkia by buying the legendary booster in the menu tab and the "Other Legendaries" gamepass for 1,150 robux.