[Since this is for D/P]
I don't really like defencive nite tbh; in D/P, you really NEED to take advantage of everything Dragonite gets over Garmunch and Gablias, so Heal Bell would be better imo
I honestly perfer mixed Dragonite; I see it as the only thing it can really do well in D/P, save Outrage + Dragon Dance
Give Dusknoir max hp ALWAYS, because HP is more important and gives you more defensive coverage on something which such amazing defences.
What with life being so Gyarados weak in D/P, I really only ever use Dusknoir with Thunderpunch.