Shellder can develop a symbiotic relationship with Slowpoke. After attaching itself to the Dopey Pokémon's tail, the two undergo a metamorphosis and together evolve into Slowbro. If it attaches to the head of a Slowpoke in possession of a King's Rock, the two will instead evolve into Slowking. These relationships allow it to travel onto land and obtain a new stage in its life cycle.