I've been playing mono water for funsies since Gen 3 and have even done so in a few VGC tournaments. But now in Gen VIII it feels like mono water is the strongest it has ever been.

My Team:

Ludicolo @ Assault Vest
Ability: Swift Swim
EVs: 252 SpA / 236 HP / 20 Speed
Modest Nature
Hydro Pump
Energy Ball
Ice Beam
Fake Out

I find with even little speed investment, Ludicolo can outspeed most things in the rain. My bulk usually surprises my opponent allowing me to survive super effective special attacks and continue my offense.

Personally as someone who runs mono water I like to run Hydro Pump over Scald. As I don't generally have good defensive typings to switch into, I prefer to play very aggressively. Occasionally a missed Hydro Pump does cause me to lose a game, but the raw power of Hydro Pump in the rain helps to keep my mono type team a real threat. Though thanks to Dynamax I can always swap to Max Geyser which can set up the rain if needed and has no accuracy check!

Energy Ball is my grass stab move of choice. Giga Drain is close in power, but I prefer to have something with as much oomph as possible. Leaf Storm is a tad too much, a misprediction on my opponent's switches could lead to my Ludicolo becoming dead weight. Grass coverage generally doesn't help in most MUs, but is essential for fighting Gastrodon and can help out when I'm worried Hydro Pump might miss a low health Pokemon.

Ice Beam is for coverage against the many Dragons running around. Duraludon is especially tough for my team to deal with, but more times than not my Ludicolo is able to tank Duraludons hits and knock the big boy out with Ice Beams with a little support from the team.

Fake Out is always a good move to have in doubles. It can help my ally Pokemon to set up or prevent my opponent from setting up themselves. I mainly use Fake Out to stop Whimsicotts or Grimmsnarls from doing anything while my ally knocks that Pokemon out. In Dynamax this move becomes Max Strike, which deals very little damage but is once in a blue moon useful for speed control.

Pelipper @ Focus Sash
Ability: Drizzle
EVs: 252 HP / 252 SpA / 4 Def
Modest Nature
- Surf
- Hurricane
- Tailwind
- Protect

Pelipper is Ludicolo's partner in crime, the two of them being my leads into most match ups. Obviously Drizzle powers up the entire team so it's quite essential to have around. But that doesn't mean Pelipper can't get some KOs itself.

I used to run Hydro Pump on my Pelipper in the past, but as I moved up the ranks I kept running into Trick Room teams. Surf has been essential for getting the finishing blow on Focus Sash Pokemon and/or those hiding behind Follow Me. Unfortunately I deal a bit of damage to my allies, but ever since I made this swap I've had an extremely high win rate against Trick Rooms so I gotta say I think it was a good choice.

Hurricane is a powerful Flying type STAB move that allows me to deal with pesky Grass types. And to be perfectly honest the confusion chance has saved me a few times in games that should have been losses. The fact that this move becomes Dynamax Airstream is also very beneficial as it gives me even more speed control in a meta where tail wind is everywhere. Speaking of which Pelipper's own Tail Wind is ideally used to counteract my opponent's Tail Wind or simply set up my team with an extreme advantage.

Lastly I run Protect to hopefully buy time while an Electric type Pokemon is in. Pelipper's x4 weakness to electricity is like a Lightning Rod that allures many of my opponents to click into the bird. Between Protect and Focus Sash I can usually buy the time I need to gain control of the situation.

Rotom-Wash @ Sitrus Berry
Ability: Levitate
EVs: 252 HP / 252 SpDef / 4 Def
Calm Nature
-Hydro Pump
-Thunder
-Will-O-Wisp
-Protect

Now while nearly all of my team are meant to be played as offensively as possible, Rotom-Wash is invested purely into defense. In a meta where grass type Pokemon are rather rare, my team mostly fears Electric type attacks coming in on it which this little Rotom can withstand.

Now if it was only Electric attacks I was afraid of than the better pick for this slot would definitely be Seismitoad, but this Rotom wants to also protect its team from strong physical threats. Will-O-Wisp is such a strong move in a meta with lots of physical attackers that have no means of protecting themselves from burns. Dracovish, Braviary, Lucario, and many other attackers find themselves in an odd spot once their attack had been reduced to half.

Dracovish @ Lum Berry
Ability: Strong Jaw
EVs: 252 Atk / 156 HP / 100 Speed
Adamant Nature
-Fishious Rend
-Crunch
-Leech Life
-Protect

The big fish itself is probably my favorite Pokemon of this generation, despite most of my KOs actually coming from Ludicolo. This thing demands so much respect that it is usually my opponent's target the second it is able to hit the field. I run Lum Berry rather than Choice Band/Scarf because it gives me more options rather than making it easy for my opponent to lock me into an attack and play around it. My opponents usually waste a turn hitting into protect and possibly another turn trying to land a Thunder Wave or Will-O-Wisp.

Due to Tail Wind, Dracovish is usually able to get off Fishous Rends without a problem. Plus with rain support it can hit very powerfully into any Pokemon, including those that resist water attacks.

Originally I ran Dragon Rush, but the number of games I lost to that move missing made me decide to toss that attack to the side. I've found much more value in my other attacks, especially Leech Life which allows me to hit into Rotom-Mow for SE damage.

Gyarados @ Life Orb
Ability: Intimidate
EVs: 252 Atk / 252 Speed / 4 Def
Adamant Nature
-Aqua Tail
-Power Whip
-Bounce
-Protect

My top 4 Pokemon are the ones who are used in most MUs. But if I ever notice a lack of electric type users then Gyarados gets to join the party. Generally I find the teams with no electric coverage tend to be physically oriented so I prefer Intimidate over Moxie as my team can be a bit physically frail.

Aside from that this is just your typical Gyarados. The Power Whip is definitely essential for dealing with Gastrodon as it can usually OHKO even with the Rindo Berry.

Barraskewda @ Luminous Moss
Ability: Propeller Tail
EVs: 252 Atk / 252 Speed / 4 Def
Jolly Nature
-Liquidation
-Close Combat
-Crunch
-Poison Jab

This beautiful Pokemon is an automatic pick against any Trick Room attempting to set up behind Follow Me. There have been so many games where my opponent has forfeit Turn 2 because they didn't know what Propeller Tail is. This ability allows Barraskewda to target whoever he wants despite Follow Me, Rage Powder, or Storm Drain trying to redirect my attack.

Against Hatterene Indeedee my Barraskewda is able to OHKO the trick room user in the rain. Against Bronzong I find that Max Geyser Pelipper's Surf will knock that big thing out before it can activate it's trick room. The Surf does unfortunately hit my Barraskewda so without much thought put into this choice I tossed Luminous Moss onto the big fishy. Oddly enough the Special Defense increase has allowed it to live just a bit longer in a few situations, so it feels like a decent enough choice. My other attacks are simply coverage, but it is always nice having a Dynamax Pokemon that can boost its partner be it physical or special.

Leads

As I said above I generally lead Ludicolo and Pelipper as they can deal with such a wide array of Pokemon while setting up Dracovish in the back. Barraskewda and Pelipper are obviously my Trick Room stoppers as I also just mentioned. Though in particularly odd MUs I'll start Ludicolo and Rotom to try and set up some burns to protect the team.

Issues for this team

Gastrodon I've mentioned this Pokemon a few times so you may have picked up that gives me a lot of trouble. This team wants to just click the water button into most things and Gastrodon is there to shut that down. With Ludicolo and Gyarados having Power Whip I do have a couple answers, I just need to make sure to not lose them too early as many Gastrodons are usually lurking in the back of their teams.

Goodra I honestly don't really have anything to fight this thing. It's exceptionally rare, but when I do come across hit the thing resists almost all of my attacks. That said, Dracovish can still take care of it with the right support.

Jellicent is a trick room setter I can't actually stop. The thing absorbs water and is bulky enough to take any coverage hit I can dish out. Super rare, but hey some MUs are gonna be bad.

Some videos of my matches:

Barraskewda and Pelipper busting up Rank's favorite Trick Room team!

https://youtu.be/ngvtmgYunDI

Ludicolo and Pelipper just putting in the work!

https://www.youtube.com/watch?v=TV0Nml2tnEo