King's rock - gives any move a chance to make the target flinch
Wide Lens - boosts accuracy of moves by 10%
Persim berry/Lum berry - snaps the user of Outrage out of confusion
Nature - any +attack nature will do fine, as long as the Spec. Attack stat is NOT lowered as a result of having this nature.
Move #1.Outrage/Dragon Rush - Outrage is an extremely powerful move, and with stab has a base power of 180, however, this move locks you into the attack for 2-3 turns and confuses Hydreigon after its used, so make DAMN sure that you have a persim bery or a lum bery as a held item, or plenty of medicine to back Hydreigon up, because missing an attack, AND hurting yourself in the same turn isn't the best idea when in a strategic battle. A And its your choice whether to have the wide lens to boost Dragon Rush's Accuracy, or the King's rock to give it a higher chance of making your target flinch. Dragon Rush has a base power of 100, but stab makes it 150, but other tan that its not all that special of a move.
Move #2.Dragon Pulse - This move has a power of 90, but with stab has a base power of 135, but has no other added effects other than flinching, but only if you hold the king's rock.
Move #3.Dark Pulse - This move has a base power of 80, and with stab has a base power of 120. having this move, as well as having it paired with the king's rock, can make for a challenging battle for your opponent, because they'll flinch so often that they won't be able to attack you every turn.
Move #4.FlameThrower/Fire Blast - Fire Blast has a base power of 120, but low accuracy (85) and 5 PP. Flame Thrower in my opinion is the better choice because its accuracy is at 100% and can be used 15 times, as well as having a base power of 95. Both of these moves are super effective against both bug and ice type pokmon, which are super effective against a dark and dragon type like Hydreigon.