Mystery at the Lighthouse

The party emerges from the forest onto a beach, where in the distance they see a lighthouse, shining at the tops of a cliff. The lighthouse belongs to Bill, a Pokémon researcher who is awaiting the coming of a one-of-a-kind Pokémon, never before seen by humans. Before long, a tremendously large shadow begins to take form in the sea mists, but this possible discovery could be hindered due to the infamous Team Rocket lurking in the background cooking up another one of their schemes. Could such a legendary Pokémon truly exist?