Imagine you and your pokemon are chilling out in the wild, having a picnic, and suddenly, a dark portal opens in a field nearby your location and a huge serpent dragon pokemon with black extensions and red spikes at the end of them comes out of it. It's as big as a skyscraper and it proceeds to roam around the area looking for food. It scoops up and devours a herd of herbivore pokemon before opening another dark portal and diving back into it. And you just witnessed all of it.