Show Me the Metal!

Some mysterious and unknown Pokémon have arrived on Melemele Island, and they eat metal! They start wreaking havoc across the island, including eating the tools at the Pokémon School, the equipment in the Ultra Guardians' headquarters and even James's precious bottle cap collection. James is enraged and decides to chase down the Pokémon to get his revenge. Just who and what are they and why is one of them hanging around Ash's Rowlet?