The Mystery Menace

In the city of Trovitopolis, our heroes find themselves in an underground tunnel, where a mysterious creature captures Ash's Bulbasaur. The conceited Mayor wants the sewer creature destroyed, but our heroes realize that it may be a new Pokemon, and attempt to safely capture it. They discover that it's just an oversized Bulbasaur, in need of some company. Apparently, Bulbasaur was abandoned by its master for not evolving, and that master is none other than the Mayor himself!