Hydreigon: Horrible. This is a Special Sweeper Hydreigon right? Then you need to put sweeper EV's on it! Most sweepers aren't designed to take hits. They are designed to hit hard, and switch out(If they have a choice item.The max speed you can have without any EV's invested is I believe 254. You will not outspeed anything with that! What's the good of having an amazing special sweeper if you can't hit anything before dying? Your moveset is really good. Your EV's must be 4 HP / 252 SAtk / 252 Spd. if you run timid, then choice specs is fine, but I recommend modest with Choice Scarf. Your choice!
Braviary: A Muscle Band is no good. Give it a life orb. Fly is no good as it allows the opponent a free switch or set-up. Use Brave Bird in it's place. If your concerned about recoil, go with aerial ace.
Serperior: Very nice, but no need for Energy Ball and Giga Drain. Instead of Energy Ball, use Leech Seed. Then you can choose between Energy Ball and Giga Drain. Power or more Healing. Up to You. On to the item. Wise Glasses suck. Go for leftovers or something.
Samurott: Fine, but get rid of Scald for Rest, filling it's role as a Bulky Water. Give it a chesto berry for instant awake.
Emboar: Nice, except since Hydreigon needs the Choice Scarf more than Emboar, since Emboar is a bit Bulkier. Choice Band FTW!
For your sixth pokemon try Reuniclus. Here is your final team.
Hydreigon @ Choice Scarf
4 HP, 252 SAtk , 252 Spd
-Focus Blast / Surf
Braviary @ Life Orb
Ability: Sheer Force
4 HP, 252 Atk, 252 Spd
-Brave Bird / Aerial Ace
Serperior @ Leftovers
4 HP, 252 SpAtk, 252 Spd
-Energy Ball / Giga Drain
Samurott @ Chesto Berry
4 HP, 126 Def, 252 SpAtk, 126 SpDef
Emboar @ Choice Band
252 HP, 252 Atk, 4 Spd
Reuniclus @ Lagging Tail
Ability: Magic Guard
EVs: 172 Def / 168 SAtk / 168 SDef
This set ruins any sweeper. Trick the Lagging Tail onto them. Psychic and Shadow Ball are STAB and Coverage, respectively. Recover is recovery. Simple enough. These EV's give it enough bulk to survive a hit before Tricking the Lagging Tail on. Then he can hit pretty hard.
Hope this helps, and good luck battling!