Lumineon
Swift Swim
Speed doubles in rain.
Storm Drain
All Water attacks hit this Pokémon.
Type Tier
Water UU
Statistics
Min- Min Max Max+
HP
69
 - 279 342 -
Atk
69
 156 174 237 260
Def
76
 169 188 251 276
SpA
69
 156 174 237 260
SpD
86
 187 208 271 298
Spe
91
 196 218 281 309
Name Item Ability Nature

Rain Dance

 Life Orb Swift Swim Modest
Moveset EVs
~ Rain Dance
~ Surf
~ Hidden Power Grass / Hidden Power Electric
~ Ice Beam
252 HP / 6 Def / 252 SpA

This is your best chance with Lumineon. Its defenses aren't too bad, so use Rain Dance to double your Speed and power up Surf. Even with a mere 260 Special Attack, Surf stands to do good damage. Hidden Power will hit other Water-types (Grass won't hurt Pelipper, and Electric won't hurt Water/Ground-types) while Ice Beam deals with Grass-types and Dragons. Life Orb gives a little extra power to these moves, so you can hopefully kill a few things before dying.

Other Options

Safeguard is a support option. Charm might force switches. U-turn is useful as always.

EVs

Modest nature with maxed out Special Attack and HP. Rain Dance provides all the Speed he requires.

Opinion

Inferior to Seaking, of all things. It does work in NU, but is outclassed in UU.

Counters

Resist Water, and you're a Lumineon counter. That's about all there is to say here.