Mystery at the Lighthouse

S1, E13: The party emerges from the forest onto a beach, where in the distance they see a lighthouse shining at the top of a cliff. The lighthouse belongs to McKenzie, 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 trio lurking in the background cooking up another one of their schemes. Could such a Pokémon truly exist?