Kingdra

Swift Swim
Speed doubles in rain.
Type Tier
Water / Dragon BL
Statistics
Min- Min Max Max+
HP
75
- 291 354 -
Atk
95
203 226 289 317
Def
95
203 226 289 317
SpA
95
203 226 289 317
SpD
95
203 226 289 317
Spe
85
185 206 269 295
Name Item Nature

Rain Dancer

Leftovers Modest
Moveset EVs
~ Rain Dance
~ Surf / Hydro Pump
~ Ice Beam
~ Toxic / Hidden Power Electric
240 HP / 252 SpA / 16 Spe

Basic Rain Dancer set. Kingdra has decent defensive stats, but can't really damage much. Toxic is for Milotic and Thick Fat Snorlax. Hidden Power Electric is a good choice to hit Water types like Milotic somewhat, but also covers Gyarados.

Name Item Nature

Flailer

Liechi Berry Lonely
Moveset EVs
~ Substitute / Endure
~ Flail
~ Dragon Dance
~ Hydro Pump
252 Atk / 4 SpD / 252 Spe

If you can get a switch to Dragon Dance on, Flail should damage a lot of their team. For Skarmory / Weezing / Gengar and friends, Hydro Pump them into oblivion.

Other Options

It can Rest, or use Dragonbreath for Paralysis.

EVs

For the Rain Dance set, you should always max Special Attack, and then probably max HP. It needs no Speed, because after Rain Dance is in effect, you'll be at 412 Speed, which is faster than anything but Ninjask and some Electrode. If you really want, you can use 16 Speed EVs, as this will guarantee you are faster than Jolly Marowak before a Rain Dance, and you'll beat Adamant Ninjask after a Rain Dance. You probably shouldn't be worried about Jolly Ninjask, but, if you really want, you can bring Kingdra to 230 Speed, which requires 96 EVs. The Flail set should have 264 Speed minimum with Substitute, max Attack, and any leftover EVs into Special Defense to make your Substitutes unbreakable by Ice Beam. You can use no Speed if you have Endure, as you can Dragon Dance more, at the risk of taking status.

Opinion

Kingdra isn't seen much, due to the prevalence of Pokémon like Blissey, Milotic, and Suicune, who wall it all day, potentially setting up a Calm Mind sweep.

Counters

Snorlax, Blissey, and Regice wall it just like they wall almost any Special Attacker. Celebi can kind of stop it because it resists Surf, and, although it's weak to Ice Beam, Kingdra doesn't have the Special Attack to really hurt it too much. A Celebi with 404 HP (252 EVs) and 240 Special Defense (16 EVs) is 3HKOed by Modest Kingdra Ice Beam, giving it plenty of time to set up a Calm Mind or Leech Seed Kingdra. Gyarados and Suicune can easily come in (although Gyarados has to worry about Hidden Power Electric) and set up a Dragon Dance or Calm Mind sweep, respectively. Milotic, although it lacks a set up move, still walls Kingdra's hits with its high Special Defense and Recover, and can just slowly wear it down with Ice Beam. Ludicolo and Vaporeon are much of the same.