Okirua

Destiny Knot takes 5 IVs from both parents, 3 from one and 2 from the other. Power Items just make a guaranteed IV, but it have higher chance of 6 IVs. But you don't necessarily need 6 IVs for most of the Pokemon. Bronzong is bad with 31 Speed IV, Machamp doesn't need to have 31 Sp. Atk IV and if you put 31 Attack IV for a Hydreigon, it will hit itself harder when its opponent uses Swagger. In the case of the Hydreigon, you can make a Physical or Special Attacker, but the latter is better. I recommend 0 Speed IV for Trick Room users or 0 Attack IV for Special Attackers or 0 IVs for both stats if you are using both strategies, like the Reuniclus. For a Mixed Attacker, I'd recommend 31 IVs in all the 6 IVs, but as I said, don't put 31 IV in Speed if the Pokemon is slow and can be useful in Trick Room.

I hope it helped.