My first team plan in SS was to catch a Sentret, as my Crystal version had an Ice punching Furret as a team member. I started playing SS in the afternoon, though, so I never saw Sentret. As I was walking with Leaf Guy the Chikorita near Dark Cave, a Ratatta appeared. I saw Ratatta before, but this one seemed different, like it was calling out to me. I decided that I wanted to catch it. I then caught it with a Pokeball, and Mouser, now a Raticate, has been on my team ever sense.