Possibly the worst team I've made...but I like it.

[Sonata]

Possibly the worst team I've ever made in OU, but I kinda like it because it's a change from the same old that I always use. But I need to make it better since I don't always win like I'm supposed to. I started the team with just Starmie, Crobat, and Skarmory. I lead Skarmory and get all the hazards then whirlwind til I die or until I can give Starmie a chance to get in without dying, then spam whirlwind with Crobat and get outsped by pokemon with half of its speed. What. I tossed in Gengar because I got tired of people trying to stat boost as I was hazarding and then I just tossed Destiny Bond on him, Tentacruel is for the poisonous things and Espeon is another attacker.

Starmie @ Leftovers
Ability: Natural Cure
EVs: 252 Spd / 252 SAtk / 4 SDef
Timid Nature
- Hydro Pump
- Thunderbolt
- Ice Beam
- Rapid Spin

Crobat @ Black Sludge
Ability: Infiltrator
EVs: 252 Spd / 128 Def / 128 SDef
Jolly Nature
- Roost
- Whirlwind
- Brave Bird
- Super Fang

Skarmory @ Leftovers
Ability: Sturdy
EVs: 160 Def / 252 HP / 96 SDef
Bold Nature
- Spikes
- Stealth Rock
- Roost
- Whirlwind

Gengar @ Black Sludge
Ability: Levitate
EVs: 252 Spd / 252 HP / 4 SAtk
Timid Nature
- Sludge Bomb
- Clear Smog
- Confuse Ray
- Destiny Bond

Tentacruel @ Black Sludge
Ability: Liquid Ooze
EVs: 252 HP / 252 Spd / 4 Spa
Hasty Nature
- Confuse Ray
- Acid Spray
- Toxic Spikes
- Toxic

Espeon @ Life Orb
Ability: Magic Bounce
EVs: 252 Spd / 252 SAtk / 4 HP
Timid Nature
- Dazzling Gleam
- Psychic
- Shadow Ball
- Signal Beam

 

[PlatinumDude]

Having Crobat and Skarmory together is redundant, IMO, as both fulfill the same role as a Whirlwinder. Crobat's best role in OU is a Defogger, but you already have Starmie to clear away hazards. You seriously lack ways to deal with Steel Pokemon. For this reason, I'd replace Crobat with a strong Fire Pokemon like Infernape, Charizard, Talonflame or Heatran:

Charizard:
-Dragon Dance
-Flare Blitz/Fire Punch
-Dragon Claw/Outrage
-Earthquake/Roost
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Charizardite X
Ability: Blaze

or
-Dragon Dance
-Dragon Claw
-Fire Punch/Earthquake
-Roost
Nature: Adamant
EVs: 144 HP/244 Atk/120 Spe
Item: Charizardite X
Ability: Blaze

or
-Fire Punch/Earthquake
-Dragon Claw
-Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/148 SDef/112 Spe
Item: Charizardite X
Ability: Blaze

or
-Fire Blast
-Solar Beam
-Focus Blast
-Dragon Pulse/Roost
Nature: Timid/Modest
EVs: 4 Def/252 SAtk/252 Spe
Item: Charizardite Y

Infernape:
-Fire Blast/Flare Blitz
-Close Combat
-Thunder Punch
-Grass Knot/Mach Punch/Hidden Power (Ice)
Nature: Hasty/Naive
EVs: 168 Atk/88 SAtk/252 Spe
Item: Life Orb/Expert Belt

Talonflame:
-Swords Dance
-Flare Blitz
-Brave Bird
-Roost
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Sharp Beak/Sky Plate
Ability: Gale Wings

or
-Flare Blitz
-Brave Bird
-U-turn
-Tailwind/Roost
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band/Sharp Beak/Sky Plate
Ability: Gale Wings

or
-Bulk Up
-Brave Bird
-Taunt/Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Gale Wings

Heatran:
-Lave Plume
-Protect
-Taunt/Roar/Stealth Rock
-Toxic/Will-o-Wisp
Nature: Calm
EVs: 248 HP/220 SDef/20 Spe
Item: Leftovers

or
-Fire Blast/Overheat
-Flash Cannon
-Earth Power/Stone Edge
-Flamethrower/Fire Blast/Hidden Power (Ice)
Nature: Modest
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Specs/Choice Scarf

If you still want a phazer alongside Skarmory on the team, I'd recommend using Zygarde for this role, as it can deal with non-Skarmory Steel Pokemon with Earthquake:
-Substitute
-Glare
-Dragon Tail
-Earthquake
Nature: Impish
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers

There seriously is no need to put 2 hazards on Skarmory, as it becomes a sitting duck otherwise if you plant to sit there for 4 turns to get all 4 layers up. It's best to stick to one only. What KOs does your EV spread avoid?:
-Whirlwind
-Roost
-Stealth Rock/Spikes
-Brave Bird
Nature: Impish
EVs: 252 HP/252 Def/4 SDef or 252 HP/16 Def/240 SDef
Item: Leftovers/Rocky Helmet
Ability: Sturdy

You're squandering Gengar's wide special move pool, as you only have Poison moves for offensive moves, making it walled by Steels entirely. It's too frail to use Clear Smog; Amoonguss does that better because it's bulkier. Relying on confusion to annoy opponents is not good. Give Gengar more coverage moves:
-Shadow Ball
-Sludge Bomb
-Focus Blast/Thunderbolt
-Destiny Bond
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb

Tentacruel has to go. Its best niche was a Rapid Spinner able to absorb Toxic Spikes, but it's seriously fallen out of favor because it struggles against top OU threats like Aegislash. Scolipede is a better alternative, IMO, since it has the option to deal with Steel Pokemon with Earthquake:
-Megahorn
-Spikes
-Swords Dance
-Baton Pass/Earthquake/Rock Slide
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Focus Sash
Ability: Speed Boost

or
-Megahorn
-Poison Jab/Rock Slide
-Earthquake
-Protect
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb
Ability: Speed Boost

Offensive Espeon is outclassed by Speed Deoxys, Latios, Alakazam and Mega Medicham because those Pokemon have better coverage options. It's best used as a Dual Screener:
-Reflect
-Light Screen
-Baton Pass
-Yawn/Psychic/Psyshock
Nature: Timid
EVs: 252 HP/4 Def/252 Spe
Item: Light Clay
Ability: Magic Bounce

If you want an offensive Psychic Pokemon, use the Psychics I mentioned:

Speed Deoxys:
-Psycho Boost
-Ice Beam
-Superpower
-Knock Off/Stealth Rock
Nature: Hasty/Naive
EVs: 20 Atk/252 SAtk/236 Spe
Item: Life Orb

Alakazam:
-Psychic/Psyshock
-Shadow Ball
-Focus Blast
-Hidden Power (Ice)/Dazzling Gleam/Thunder Wave
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Focus Sash
Ability: Magic Guard

or
-Psychic/Psyshock
-Shadow Ball/Hidden Power (Fire)
-Focus Blast
-Taunt
Nature: Modest
EVs: 4 HP/252 SAtk/252 Spe
Item: Alakazite
Ability: Magic Guard

Latios:
-Draco Meteor
-Psyshock
-Earthquake/Thunderbolt/Hidden Power (Fighting)
-Defog/Recover/Roost
Nature: Hasty/Timid
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb

Medicham:
-High Jump Kick
-Zen Headbutt
-Ice Punch/Fire Punch
-Fake Out/Substitute
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Medichamite
Ability: Pure Power