Just something to note about me, when I play a monotype team, I go 6-0 because it is more fun for me that way. I enjoy the challenge but I am appreciate of any criticisms and advise that you may have for me. Below are my pokemon in no particular order except for the lead. I give a brief description on any move-set that is not overly obvious and I do not always use set EVs. I'll use whatever I need and works best for my team. That'll usually also be included in the description.
Tentacruel (Irukandji)
Ability: Clear Body
Nature: Calm
EVs: 252 Hp / 180 Def / 76 SpA
Item: Choice Scarf
Moveset: Toxic Spikes, Rapid Spin, Sludge Bomb, Hydro Pump
Azumarill (Neptune)
Ability: Huge Power
Nature: Adamant
EVs: 240 Hp / 252 Atk / 16 Spe
Item: Choice Band
Moveset: Aqua Jet, Ice Punch, Superpower, Double Edge
Kingdra (Poseidon)
Ability: Swift Swim
Nature: Naughty
EVs: 252 Atk / 240 SpA / 16 Spe
Item: Life Orb
Moveset: Rain Dance, Draco Meteor, Waterfall, Hydro Pump
Suicune (Boreas)
Ability: Pressure
Nature: Bold
EVs: 252 Hp / 252 Def / 4 SpD
Item: Leftovers
Moveset: Rest, Calm Mind, Surf, Hidden Power (Electric)
Milotic (Siren)
Ability: Marvel Scale
Nature: Calm
EVs: 252 Hp / 252 Def / 4 SpA
Item: Leftovers
Moveset: Recover, Rain Dance, Surf, Ice Beam
Starmie (Trident)
Ability: Natural Cure
Nature: Timid
EVs: 4 Hp / 252 SpA / 252 Spe
Item: Life Orb
Moveset: Hydro Pump, Thunder, Ice Beam, Recover

Tentacruel (Irukandji)
Ability: Clear Body
Nature: Calm
EVs: 252 Hp / 180 Def / 76 SpA
Item: Choice Scarf
Moveset: Toxic Spikes, Rapid Spin, Sludge Bomb, Hydro Pump
Changes: Hidden Power (Dark) -> Rapid Spin
I know that a lot of people probably will not like it, but I run my Tentacruel with Choice Scarf. The reason being that the most common lead pokemon that give it trouble: Aerodactyl, certain Infernape, and Azelf can be problematic because they're faster. Two of the three hit Tentacruel with physical moves so that's where I am investing its defensive EVs. If Azelf comes out, I can take the chance of hitting it with Hidden Power Dark, switching out, or doing whatever. Aerodactyl and Infernape will fall to Hydro Pump without Focus Sash and will switch out after they question why I am faster. If a lead comes out that I can handle, I'll use Toxic Spikes and try to set my team up. The majority of my team either abuses recovery moves or heavy hitting moves that would usually leave someone barely alive but in my case Toxic Spikes would make them useless or revenge kill-able with Azumarill.

Azumarill (Neptune)
Ability: Huge Power
Nature: Adamant
EVs: 240 Hp / 252 Atk / 16 Spe
Item: Choice Band
Moveset: Aqua Jet, Ice Punch, Superpower, Double Edge
Neptune's job is to pick things off with Aqua Jet, hopefully after Rain Dance and Toxic Spikes. It functions as a late game sweeper and an early game revenge killer. I opted out of Waterfall for more coverage because with Rain Dance Aqua Jet should do more than enough damage to wreck any frail pokemon and most healthy pokemon.

Kingdra (Poseidon)
Ability: Swift Swim
Nature: Naughty
EVs: 252 Atk / 240 SpA / 16 Spe
Item: Life Orb
Moveset: Rain Dance, Draco Meteor, Waterfall, Hydro Pump
Poseidon is usually the turn around pokemon if this team is losing. It can smash walls and kill any special sweet that comes into play. His EVs are pretty obvious and with Life Orb you can imagine the damage. I have given him Rain Dance in case it is not already in effect or about to run out. With Toxic Spikes things really get interesting because most pokemon that can manage to survive two hits usually do so with 11% or less. Toxic Spikes functions to get rid of these pokemon.

Suicune (Boreas)
Ability: Pressure
Nature: Bold
EVs: 252 Hp / 252 Def / 4 SpD
Item: Leftovers
Moveset: Rest, Calm Mind, Surf, Hidden Power (Electric)
Changes: Roar -> Hidden Power Electric
Boreas is a pokemon that I had a lot of positive experiences with. I think that the moveset and EVs are all the most common so I do not need to explain too much except for having Roar and not another attacking move. Basically, I'm seeing Boreas stalling most pokemon out with Rest and Calm Mind then tearing them apart using Surf. Roar is there to shuffle things for Toxic Spikes, screw with stat ups, or knock away bad match-ups. I have been considering replacing Roar with Hidden Power (Ground or Fighting), Ice Beam, or Toxic but I am not too sure; perhaps someone could convince me into one of them. Hidden Power Fighting was considered for Tyranitar who can be a pain.

Milotic (Siren)
Ability: Marvel Scale
Nature: Calm
EVs: 252 Hp / 252 Def / 4 SpA
Item: Leftovers
Moveset: Recover, Rain Dance, Surf, Ice Beam
Siren is one of my sturdier Rain Dancers. Rain Dance then switch off into something dangerous or stay in and take some abuse. Siren packs Hidden Power (Fire) for Steel pokemon that can be troublesome such as Bronzong, Lucario, and Magnizone. It also allows me to pick off pokemon like Celebi who are bulky yet beastly.
Changes: Hidden Power (Fire) -> Ice Beam

Starmie (Trident)
Ability: Natural Cure
Nature: Timid
EVs: 4 Hp / 252 SpA / 252 Spe
Item: Life Orb
Moveset: Hydro Pump, Thunder, Ice Beam, Recover
Change: Expert Belt -> Life Orb
Change: Thunder Bolt -> Thunder
Change: Thunder Bolt -> Thunder
Trident is my last pokemon and primarily here for type coverage and Expert Belt abuse. It does a good job of cleaning up troublesome pokemon and helping me prepare for lategame.