I own halo 5, the master chief collection and have the halo nightfall bluray disc but for some reason when ever watch it it wont let me get the nightfall armour on halo 5
You can’t get the armour by watching the DVD I’m afraid OP, that promotion is only available to those who purchase and watch the Halo Channel version. The promotion itself may have ended now, but the armour is in the general REQ pool so you can get it by opening Gold packs 
thank you