Ok, here's how it goes,
1) Have Natu/Xatu (Male) learn Wish;
2) Breed it with female Togetic/Togekiss to get a male Togepi with Wish;
3) Evolve that Togepi to a Togetic;
4) Breed it with female Pikachu/Raichu to get a male Pichu with Wish;
5) Evolve that Pichu to a Pikachu;
6) Breed it with female Eevee/Leafeon/Glaceon/Umbreon/Vaporeon/Flareon/Jolteon/Espeon to get an Eevee with Wish; and finally
7) Evolve that Eevee to an Umbreon, and just like that you have Wish Umbreon.
This is one of the many chain-bred Pokémon; in fact this is one that involves Pikachu.
1) Have Natu/Xatu (Male) learn Wish;
2) Breed it with female Togetic/Togekiss to get a male Togepi with Wish;
3) Evolve that Togepi to a Togetic;
4) Breed it with female Pikachu/Raichu to get a male Pichu with Wish;
5) Evolve that Pichu to a Pikachu;
6) Breed it with female Eevee/Leafeon/Glaceon/Umbreon/Vaporeon/Flareon/Jolteon/Espeon to get an Eevee with Wish; and finally
7) Evolve that Eevee to an Umbreon, and just like that you have Wish Umbreon.
This is one of the many chain-bred Pokémon; in fact this is one that involves Pikachu.