All right, I'm brand new to competitive battling, so I'm open to any suggestions! Here's my Rain Team. (I know. Another Rain Team.)
Politoed @ Leftovers
Ability: Drizzle
Bold Nature
EVs: 252 HP / 252 Def / 4 Spe
-Scald
-Ice Beam
-Protect
-Toxic
The point of Politoed is to get the rain out, obviously, so he's bulky in order to make sure the rain stays out for the entire battle. Scald's a good STAB move with a chance to burn, which is always nice, Ice Beam is for type coverage, and Toxic and Protect go hand and hand. Poison your opponent and stall it out. Politoed probably won't see much action, though; he'll lead and then switch out until he's needed.
Jirachi @ Leftovers
Ability: Serene Grace
Timid Nature
EVs: 252 HP / 4 SpA / 252 Spe
-Substitute
-Calm Mind
-Thunder
-Psyshock
Jirachi's popular SubCM set is pretty self-explanitory. You send Jirachi in on an attack which you predict will be either resisted or a support move, and then you set up your Substitute. Set up a couple Calm Minds, and then attack. Thunder gets 100% accuracy in the rain, and Psyshock's a powerful STAB move.
Toxicroak @ Black Sludge
Ability: Dry Skin
Adamant Nature
EVs: 244 HP / 252 Atk / 12 Def
-Bulk Up
-Substitute
-Drain Punch
-Sucker Punch
Toxicroak gets benefited from the rain with its superb Dry Skin ability. It provides more type-coverage for the team and is also a physical attacker who shatters through Special Walls that otherwise cripple the rest of the team. His moveset is similar to Jirachi's; after he sets up a few Bulk Ups under a Substitute. Drain Punch is STAB and recovers some HP sacrificed for the Substitutes, and Sucker Punch is for type coverage and a nice priority move.
Keldeo @ Choice Scarf
Ability: Justified
Timid Nature
EVs: 4 HP / 252 SpA / 252 Spe
-Surf
-Hydro Pump
-Hidden Power [Ice]
-Secret Sword
Keldeo is the star of the team. His Choice Scarf will allow him to outspeed most Pokemon in the OU tier, and his Special Attack is maxed out to deal massive damage against his opponents. Surf and Hydro Pump are, yes, both Water-type moves. Surf has 100% accuracy, but Hydro Pump sacrifices a little accuracy for more power, so the chosen move will depend on who's out. Hidden Power Ice provides type coverage, and Secret Sword is a good STAB move to have.
Volcarona @ Life Orb
Ability: Flame Body
Modest Nature
EVs: 252 SpA / 4 SpD / 252 Spe
-Quiver Dance
-Bug Buzz
-Hurricane
-Fire Blast
Volcarona surprisingly functions very well in the sun thanks to Hurricane getting 100% accuracy. Quiver Dance is a must on Volcarona, being one of the best stat-bosting moves, and Bug Buzz and Fire Blast are both STAB.
Ferrothorn @ Leftovers
Ability: Iron Barbs
Relaxed Nature
EVs: 252 HP / 88 Def / 168 SpD
IVs: 0 Spe
-Spikes
-Leech Seed
-Gyro Ball
-Power Whip
Ferrothorn's there to set up entry hazards. Rain Dance thankfully halves Fire-type moves' super-effectiveness, so they're not as big of threats. Leech Seed will sap his opponent's HP while restoring his, and he can rack up a lot with Leftovers in addition. He'll therefore be able to set up Spikes and have some way of slightly hurting his opponent at the same time. Gyro Ball and Power Whip are again, STAB. Gyro Ball does a ton of damage thanks to Ferrothorn's pathetic speed.
