That's already been discussed here.Shroomi, have you considered Knock Off vs Night Slash?
Knock Off has 5 less BP than Night Slash, but if the enemy has item that is not Mega Stone, the damage is boosted by 50%.
Granted Night Slash has higher critical hit chance, but the utility from Knock Off imo is far more useful than small crit chance boost.
As I said right at the top in the cons section, Knock Off is illegal... otherwise it would already be in the set.
Knock Off is illegal until Pokebank, at which point it will definitely replace Night Slash.