Competitive Team Help

I just want to know if there can be any improvements to my team:

Tentacruel:
Ability: Clear Body
Nature: Modest
Item: Ice Gem
Toxic Spikes
Sludge Wave
Surf
Ice Beam
EV Points in: Sp. Atk- 254 Speed- 254

Haxorus:
Ability: Mold Breaker
Nature: Adamant
Item: Bright Powder
Earthquake
Dragon Claw
Brick Break
Dragon Dance
EV Points in: Def- 254 Sp. Def- 254

Cinccino
Ability: Technician
Nature: Jolly
Item: Normal Gem
Wake-Up Slap
Flail
Endure
Protect
EV Points in: Atk- 254 Speed- 254

Cofagrigus
Ability: Mummy
Nature: Modest
Item: Spell Tag
Shadow Ball
Calm Mind
Psychic
Energy Ball
EV Points in: Sp. Atk- 254 Def- 254

Serperior
Ability: Overgrow
Nature: Hardy
Item: Sky Plate
Aerial Ace
Return
Giga Drain
Growth
EV Points in: Def- 254 Sp Def- 254

Eelektross
Ability: Levitate
Nature: Modest
Item: Lum Berry
Rain Dance
Thunder
Flash Cannon
Grass Knot
EV Points in: Sp Atk- 254 HP- 254

Any advice will be helpful and they are all level 100.

252 is the optimal maximum stat to shoot for; the 4 EVs can be dumped into any stat, mainly HP for sweepers.

Tentacruel meant to be a somewhat speedy supporter:
-Toxic/Toxic Spikes Spikes
-Scald
-Rapid Spin
-Protect/Substitute
Nature: Bold
EVs: 252 HP/236 Def/20 Spe
Item: Black Sludge
Ability: Rain Dish

Or if you can't be bothered to come to the Dream World for Rain Dish Tentacool, use Jellicent instead:
-Scald/Surf
-Will-o-Wisp/Toxic
-Recover
-Taunt
Nature: Bold
EVs: 248 HP/216 Def/44 Spe
Item: Leftovers

or
-Scald/Surf
-Will-o-Wisp/Toxic
-Recover
-Shadow Ball/Ice Beam
Nature: Calm
EVs: 252 HP/36 Def/220 SDef
Item: Leftovers
Ability: Water Absorb

or
-Water Spout
-Hydro Pump/Surf/Scald
-Shadow Ball
-Ice Beam/Giga Drain
Nature: Modest
EVs: 172 HP/252 SAtk/84 Spe
Item: Choice Specs
Ability: Water Absorb

Why are you investing all your stats in defenses when Haxorus is clearly an offensive 'mon? It's frail either way:
-Dragon Dance
-Outrage
-Earthquake
-Low Kick/Taunt
Nature: Adamant
EVs: 36 HP/252 Atk/220 Spe
Item: Lum Berry/Yache Berry
Ability: Mold Breaker

or
-Outrage
-Earthquake
-Superpower
-Aqua Tail/Dragon Claw/Dual Chop
Nature: Adamant
EVs: 36 HP/252 Atk/220 Spe
Item: Choice Band
Ability: Mold Breaker

or
-Swords Dance
-Outrage
-Superpower
-Taunt/Substitute/Earthquake
Nature: Adamant
EVs: 36 HP/252 Atk/220 Spe
Item: Life Orb/Fighting Gem/Leftovers
Ability: Mold Breaker

or
-Swords Dance
-Dragon Dance
-Outrage
-Earthquake
Nature: Adamant
EVs: 36 HP/252 Atk/220 Spe
Item: Lum Berry/Draco Plate
Ability: Mold Breaker

Cinccino has more coverage moves than just Wake-up Slap. Endrevving is very hard to do with all that priority running around:
-Tail Slap
-Bullet Seed
-Rock Blast
-U-turn
Nature: Jolly/Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Choice Band/Choice Scarf
Ability: Skill Link (yes, this ability is available in-game as of B2/W2)

Never invest in a defensive stat fully without investing in HP first. Gengar can provide a more threatening offensive presence than Cofagrigus can:
-Substitute
-Disable/Pain Split/Thunderbolt/Hidden Power (Fire)
-Shadow Ball
-Focus Blast
Nature: Timid
EVs: 4 HP/252 Atk/252 Spe
Item: Black Sludge/Life Orb

or
-Shadow Ball
-Focus Blast
-Hidden Power (Fire)
-Protect
Nature: Timid
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Black Sludge

If you want to use Cofagrigus that badly, go ahead:
-Calm Mind
-Shadow Ball
-Hidden Power (Fighting)/Will-o-Wisp
-Pain Split/Rest/Will-o-Wisp
Nature: Bold
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers

or
-Shadow Ball
-Will-o-Wisp
-Haze
-Pain Split
Nature: Bold
EVs: 252 HP/136 Def/120 SDef
Item: Leftovers

Serperior is too weak offensively to do much. I think you need some hazard support in the form of Ferrothorn:
-Stealth Rock/Spikes
-Leech Seed
-Power Whip
-Gyro Ball/Thunder Wave/Protect
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers/Rocky Helmet

If you want to use Serperior that badly, its shallow offensive movepool gained more coverage options in B2/W2:
-Coil
-Leaf Blade
-Aqua Tail
-Return/Substitute
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Leftovers

or
-Calm Mind
-Giga Drain
-Hidden Power (Fire/Rock)/Dragon Pulse
-Substitute
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Leftovers

Eelektross' movepool is so freakin' wide; why aren't you making the most out of it?:
-Thunderbolt
-Flamethrower
-Giga Drain
-Superpower/Hidden Power (Ice)
Nature: Quiet/Modest
EVs: 172 HP/252 SAtk/84 Spe
Item: Leftovers/Life Orb/Expert Belt

or
-Coil
-ThunderPunch
-Drain Punch
-Dragon Tail/Aqua Tail
Nature: Adamant
EVs: 252 HP/16 Atk/240 SDef
Item: Leftovers