You live in the Kentuckea region where a lot of cool Pokémon live, you were chilling at the beach where you see the Convergent of Slowpoke, Slowpup, and Slowpup was with a Group of Kentuckian Slowpoke, The Slowpup that was with the group of Kentuckian Slowpoke was a Shiny Slowpup, So you pulled out your Rotom tablet and opened the Pokédex app and pulled out a Master Ball Rotom Tablet: "Slowpup, the Dopey dog Pokémon, a Normal/Psychic type, Although Slowpup looks like Kantonian Slowpoke, Slowpup is a completely different species, Slowpup are as slow as Slowpoke, Slowpups are the friendliest Pokémon in the Kentuckea region, and It evolves like Kantonian Slowpoke, Slowpup like the water, although Slowpup isn't a Water type, it can learn Water type moves, Making Slowpup a unique Pokémon." You threw the Master Ball at the Shiny Slowpup and you caught it because the master ball never fails to catch a Pokémon.