Personally I would use a false swiping haxorus, but since this is your game well do it your way. Zangoose is very frail, and won't be taking to many hits. It's fast, but not as fast as terrakion. It's attack is good.i would advise that you train zangoose, because he needs to be quite a few levels higher than terrakion if you want to pull this off. For natures, jolly or naive is preferable, as they both boost speed at the cost of special attack and special defense respectively. Zangoose will only be using physical attacks, so he does not mind the special attack drop, and terrakion only carries physical attacks, so zangoose won't mind the special defense drop.
Summary: With either a jolly or naive nature, zangoose will be able to outspeed terrakion and false swipe away, but I warn unless zangoose is at a very high level it will likely faint in the process. Good luck to you.