Espeon
I like your Espeon, but I don't really like the HP EVs. Change those to 252 SAtk or 128 SAtk and 128 Atk. Change the Speed EVs to 128 Def and 128 SDef so your Screens work better. If you want to stay fast so Dark types don't get you keep the nature, if not change nature to Modest/Calm/Bold. Change Psychic to Psyshock in case you run into a Special Wall like Blissey.
If you don't like that you can keep Psychic, your choice.
Forretress
I would change your EVs to 252 Def 252 HP 252 SDef. I would change Volt Switch to Explosion to destroy someone, to really destroy them hold a normal gem. I believe four of your team Bug Bite or something to actually deal solid damage.
Gyarados
Forget Bounce, Earthquake is key on Gyarados. You could change leftovers into Choice Scarf to hit Earthquake before those pesky Electric types can hurt you. Or you can have Choice Band to deal real damage. In this case Dragon Dance isn't useful. In this case leave Bounce in. Another useful item could be Life Orb where you aren't locked into moves.
Gengar
Get ride of Life Orb on Gengar and give it Black Sludge to regain HP. Also if they decide to Trick you they will get hurt from it. Change those 4 HP EVs to SDef. Change Thunderbolt to Giga Drain, it will give you more HP while still dealing with those whatever types that can be bulky. If Hidden Power Bug is for Dark and Psychic types I don't believe it would take it out. I would change that to Focus Blast to destroy them, it would also work for Steel types and Normal types that you can't touch with STAB. Substitute isn't necessary because it can be broken quickly and will take 25% of your HP. Change that to Sludge Bomb for STAB and Poison hax.
Haxorus
Change his EVs to sweeping style; 252 Atk 252 Spd 4 Hp. Give him Outrage and make him hold a Persim or Lum Berry to get rid of the confusion. Choose Brick Break over Rock Slide so that it can cover more than just Ice.
Blissey
I would change her into Chansey with Eviolite. It's defense would be doubled and would make her harder to take out with those Screens up.I would change the nature to Sassy for more Special Attack. The EVs should be 252 HP 202 SDef and 48 Def. Change Flamethrower into Seismic Toss so you get perfect 100 damage.