Pelipper @ Leftovers
Ability: Drizzle
Nature: Modest
EVs: 252HP/ 252SpA/ 4SpD
-Weather Ball
-Hurricane
-Tailwind
-Ice Beam/U-Turn
Pelipper is pretty much a staple in every water team because the rain is super useful Weather ball pairs really well under the rain, power being doubled to 100 and then another boost from the rain and STAB so it's effectively 200. Hurricane is an incredibly strong STAB move that never misses in the rain. Tailwind to have your team outspeed almost everything for 5 turns. U-turn to switch and get pelipper can set up the rain again when it's gone or Ice beam for coverage
NOTE: The reason why it's not holding a Damp Rock is because it's banned
Urshifu Rapid-Strike @ Choice Scarf
Ability: Unseen Fist
Nature: Adamant
EVs: 252Atk/ 252Spe/ 4HP
-Surging Strikes
-Iron Head
-Thunder Punch
-Fire Punch
Surging Strikes is obviously a very good move, always criting and breaks sturdy. The rest of the moves are basically just for coverage. The reason why Urshifu has no fighting moves is because it's very risky to choice scarf into a Fighting move because Fighting is resisted by 5 types and 1 type is immune to it.
Milotic @ Leftovers
Ability: Competitive
Nature: Modest
EVs: 252HP/ 252SpA/ 4 Def
-Coil
-Hydro Pump
-Ice Beam
-Recover
Now you guys may wonder "Why give a special attacker coil?" Well Flame Orb and Marvel scale is completely inferior because both coil and marvel scale raise defence, but coil doesn't require a status condition to raise defence, and slowly losing HP each turn is certainly not a good thing, so coil can just boost the defence to do the exact same thing, and the accuracy boost from coil is also extremely helpful because it allows Milotic to fire off 100% Hydro Pumps, Ice Beam is also a necessity to counter grass types and Recover will be fun for free healing.
Rotom-Wash @ Salac Berry
Ability: Levitate
Nature: Modest
EVs: 164HP/ 252 SpA/ 92Spe
-Thunder
-Hydro Pump
-Stored Power
-Nasty Plot
Rotom-Wash is most likely bulky enough to live until it gets under 25% HP for the Salac berry to activate and give it potential to outspeed many opponents including pokemon like Meowscarada, Thunder is for to never miss while Rain is still up, Hydro Pump is the only water move it knows so I have no choice, nasty plot for set up and stored power goes very well with it.
Veluza @ Sitrus Berry
Ability: Sharpness
Nature: Jolly
EVs: 252Atk/ 252Spe/ 4HP
-Fillet Away
-Subsititute
-Aqua Cutter
-Psycho Cut
Veluza is VERY underrated, Aqua Cutter and Psycho cut are great STAB moves that go well with Sharpness, Substitute to protect yourself and set up with fillet away, Raging Bolt may not be a threat because it could go for thunderclap when Veluza is gonna used Substitute and therefore making thunderclap fail, it will take the substitute out the turn Veluza uses fillet away and could go for thunderclap again, but that's when the Sitrus berry comes in clutch, having Veluza have barely enough HP to set up another substitute and dominate with his attacking moves.
Cloyster @ White Herb
Ability: Skill Link
Nature: Jolly
EVs: 252HP/ 252Atk/ 4Spe
-Icicle Spear
-Liquidation
-Drill Run
-Shell Smash
Setting up with Shell smash plus white herb removing the lowered defence makes it a really big threat, Drill Run to counter electric types and Icicle Spear to guarantee 5 hits thanks to skill link, Liquidation is also a great STAB move.