I'll Let You Evolve...

Athena is a Eevee rejected by her trainer. Her trainer wanted a shiny Eevee, and forgot about Athena as soon as she got one. One night Athena killed her trainer's Shiny Eevee and attached some of the parts onto her own body. Athena has shiny Eevee hind legs, tuft (neck), ears, tail, and a small patch on her front feet.
One day Athena was walking along Lavender Town when she saw a Shiny Eevee, with shiny Espeon ears, gem, and tail.