Mateo runs a glass and crystal shop on Sunburst lsland. His little sister Marissa lives with him and helps him run the shop. When Ash and his friends met him, he wasn't feeling very well and didn't want to make glass anymore which was hurting their business. Mateo told Ash that his creations just didn't have the spark that his Grandpa's Pokémon statues had. Mateo said he just needed some kind of inspiration and he hoped that capturing the Crystal Onix would be that spark.
Mateo used this Cloyster to battle the Crystal Onix. However, Onix was not weak against Water-type attacks and defeated Cloyster with ease.