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By SucoDeToddynho
#206081 Every time a pikachu spawns, it has a 1/1000 of being a ash cap pikachu (the one you can use the Pikashunium-Z with).

You can dyes to change the specific cap

Evolving a Greninja while having a ash cap Pikachu in your party gives him Battle Bond (only once per pikachu).
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By SKy2008
#206083 Ash cap Pikachu has been suggested many times before.

I'd keep Battle Bond Greninja to a rare encounter like we currently have with fishing. In the Pokémon games you can only acquire it fully evolved as well.