Ability: Drizzle
Nature: Modest
EVs: 252spe/ 252 sp Atk/ 4 hp
-Hydro Pump
-Focus Blast
-Hidden Power Grass
-Ice Beam
Politoed is(obviously) the rain supporter. I've always liked politoed a lot since I was young and watched the anime, and drizzle made him a top-tier pokemon. Kept alive until other weather inducers on the opposition's team are gone. The reason I run specs and not scarf is because I rarely am ever in the position where I need a scarf, and specs rain boosted STAB hydro pump with modest nature does stupid damage. Even if the pokemon resists it it'll do easily over 1/2 if they're not bulky. If they're bulky it'll do somewhere from 1/3-1/4. Other moves are for good coverage.
Ability: Torrent
Nature: Relaxed
EVs: 240 HP / 216 Def / 52 SpD
-Earthquake
-Stealth Rock
-Ice beam
-Roar
I'm still a big fan of swampert. He was my most used opener in 4th gen and a pretty good wall. I know ferrothorn can do his job and then some, but I really like roar. It's won me games. Main purpose of swampert is to counter tyranitar and set up rocks, as well as hit dragon types quite hard with ice beam.
Ability: Flame Body
Modest Nature
EVs: 252 SpA / 4 SpD / 252 Spe
~ Quiver Dance
~ Bug Buzz
~ Hurricane
~ Fire Blast
Special Sweeper. Usually sweeps late-game, even without quiver dance if their revenge killer is down. I use the drizzle setup featured here on smogon. It's proven to be really effective and completely shuts down opposing sun teams if played properly. One thing I really like about having volcarona on the team is that quite a bit of my team can take a beating from grass attacks. Often times I switch in volcarona on a grass move and it does minimal damage. If they're choiced I can set up a quiver dance and sweep or if I know they're not choiced I can just attempt to kill whatever they have out with stab bug buzz or 100% accuracy Hurricane. Fire blast is still effective on the likes of scizor and ferrothorn even in the rain due to stab and 4x damage.
Ability: Magnet Pull
Timid Nature
EVs: 4 HP / 252 SpA / 252 Spe
~ Thunderbolt
~ Flash Cannon
~ Hidden Power Fire
~ Volt Switch
Revenge Killer. I mainly run magnezone to destroy scizor and ferrothorn, but it's really good at taking out a lot of pokemon once they're weakened. HP fire is there to counter scizor and ferrothorn, even if it's weakened by rain, thunderbolt can do the job on scizor.
Ability: Skill Link
Naive Nature
EVs: 252 Atk / 4 SpA / 252 Spe
~ Shell Smash
~ Icicle Spear
~ Rock Blast
~ Hydro Pump
Physical Sweeper of the team. Cloyster is insane. I liked cloyster before too, and sometimes ran it as a wall in UU/NU in 4th gen. Shell smash is ridiculous and once I have it up, there's little that will outspeed it or live an attack from it. White herb has been really good in some situations, but sometimes I've wished I had life orb to take off that small bit of health their walls live with.
Ability: Rain Dish
Bold Nature
EVs: 252 HP / 240 Def / 16 Spe
~ Toxic Spikes
~ Rapid Spin
~ Scald
~ Protect
Just toxic spike/ spin support with some offense and good surivability. Potentially walls some pokemon. Scald does decent damage in the rain.
Let me know what you guys think, and how I could make the team better! It's tested quite well on the battle finder here, but I feel like it could improve a lot. I think my major problem is the lack of immunity to ground type attacks. Maybe Hydreigon or Latios as the revenge killer instead?