Well, there are a lot of good status moves I have in mind, so I'll list the ones I think are suited for Decidueye:
- Tailwind is a good move to raise Decidueye's Speed, therefore it will be a major threat when used. However, Decidueye's Defense is not overly high - and the Pokemon has 5 weaknesses - so you do run the risk of not being able to attack with Decidueye for the remainder of the battle after Tailwind - but it still will affect the remainder of your team.
- Feather Dance is a good move to lower to opponent's Attack, therefore it can balance off with Decidueye's moderate Defense stat.
- Toxic is always a good, reliable status move, but you do run the risk of going up against a super-effective Poison-type Pokemon, therefore making it useless. However, Toxic won't fail you the majority of the time
- Confuse Ray is another great move. It works on Normal-type Pokemon and it reduces the opponent's attacking chance to 33% for the duration of the confusion.
If it were up to me, I would give my Decidueye Confuse Ray or Tailwand, because it always plays an advantage to, not only Decidueye, but the rest of the team as well.
Hope I helped! :)