I'm moving this to Competitive Play because while it does deal with XY games, it is more focused on a competitive set rather than in-game.
The best nature for it is going to be Jolly which lowers Special Attack and raises Speed. For EVs, you will want 252 in both Speed and Attack. The last 4 can go in either defense. It isn't meant to do anything else. It has 118 base speed so it isn't really worth losing a couple Speed EVs when you could get hit right back by another Hawlucha. I definitely would recommend High Jump Kick with its 130 power plus STAB. Poison Jab can be helpful so it has a move to hit a fairy type if it absolutely has to. Just don't rely on it getting a OHKO since its Attack isn't high enough to do that.