I almost lost a match at the battle tower because a Gallade, (yes a Gallade, no imposter) had Shadow Sneak. I checked Bulbapedia and Gallade does not learn shadow sneak in any way. It is unclear if the developers wanted it this way or if someone made an error, either way this should be cleared up and potentially fixed in any future updates this game holds. (If there are any)
It gets it via breeding from Shuppet, Banette, Duskull, Dusclops, Dusknoir, Spiritomb, Pumpkaboo, and Gourgeist in gen 6.
Oh, it didnt say anything about it for gen 6 on Bulba, (I forget Insurgence isn’t on 7 yet)
It gets it via breeding in gen 7 as well, by the same pokemon with the addition of mimikyu.
just found it, damn thats overpowered