Lotus Duck has the potential to be the most potent GBU rain-abuser there is in Doubles. It was made to abuse rain in almost every way, similar to its sunny cousin Shiftry, but even moreso. Its ability, moveset, and typing are all excellent and make up for not-superb overall stats.
Ludicolo #272
->Absorb Bulb<-
Ludicolo @ Absorb Bulb / Life Orb / Lum Berry
MODEST
+Swift Swim+
4 HP / 252 SpA / 252 Spe
-Fake Out
-Hydro Pump / Scald / Surf
-Giga Drain / Grass Knot
-Ice Beam
Fake Out an undesirable opponent then proceed to get hit by Surf for paltry damage with Ludicolo's 4x Water-resistance. At that point Ludicolo will have +1 SpA and (essentially) + 2 Spd, with access to perfect coverage moves, two of which are STAB'd, one of which is also boosted by the rain. If it looks like it's possible to OHKO a foe with it, Giga Drain the HP lost from Surf back.
The choice between Hydro Pump and Scald lies in the accuracy gap, not in the Burn chance; matches played with Ludicolo are seldom matches of stall. If you choose Hydro Pump you will find that in some situations, such as against Garchomp, it will actually be wiser (if you've properly read your opponent) to use Hydro Pump, since it will hit harder than Ice Beam after a Yache Berry activates.
Lum Berry is also an option, owing to the heightened threat of a crippling Thunder Wave due to popular knowledge of Ludicolo's functionality as a Swift Swimmer.
This Ludicolo is generally used in tandem with Politoed, helping it Surf with Fake Out, but it can also switch in to another's Surf to get the boost. You may find it undesireable to have many Surf users on one team, so it may consequently be wise to use Ludicolo in one of the lead spots.

Ludicolo #272
HP: 80
Atk: 70
Def: 70
SpA: 90
SpD: 100
Spe: 70
Atk: 70
Def: 70
SpA: 90
SpD: 100
Spe: 70
PHP:
[LEFT]Level-Up Moves
-- Astonish
-- Growl
-- Mega Drain
-- Nature Power
Machine Moves
TM01 Hone Claws
TM06 Toxic
TM07 Hail
TM10 Hidden Power
TM11 Sunny Day
TM13 Ice Beam
TM14 Blizzard
TM15 Hyper Beam
TM17 Protect
TM18 Rain Dance
TM21 Frustration
TM22 SolarBeam
TM27 Return
TM31 Brick Break
TM32 Double Team
TM42 Facade
TM44 Rest
TM45 Attract
TM46 Thief
TM48 Round
TM49 Echoed Voice
TM52 Focus Blast
TM53 Energy Ball
TM55 Scald
TM56 Fling
TM68 Giga Impact
TM70 Flash
TM75 Swords Dance
TM86 Grass Knot
TM87 Swagger
TM90 Substitute
TM94 Rock Smash
HM03 Surf
HM04 Strength
HM05 Waterfall
HM06 Dive
[/LEFT]
Egg Moves
Counter
Flail
Giga Drain
Leech Seed
Razor Leaf
Sweet Scent
Synthesis
Teeter Dance
Tickle
Water Gun
Pre-evolution Moves
Mist
Natural Gift
Absorb
BubbleBeam
Zen Headbutt
Fake Out
Fury Swipes
Water Sport
Uproar
Hydro Pump
Water Pulse
Gen III Tutor Moves
(XD) Body Slam
(XD) Counter
(XD) Double-Edge
(XD) DynamicPunch
(XD) Endure
(XD) Fire Punch
(XD) Ice Punch
(XD) Icy Wind
(XD) Mega Kick
(XD) Mega Punch
(XD) Metronome
(XD) Mimic
(XD) Mud-Slap
(XD) Seismic Toss
(XD) Sleep Talk
(XD) Snore
(XD) Substitute
(XD) Swagger
(XD) Swords Dance
(XD) ThunderPunch
Gen IV Tutor Moves
(Pt/HG/SS) Dive
(Pt/HG/SS) Fire Punch
(Pt/HG/SS) Ice Punch
(Pt/HG/SS) Icy Wind
(Pt/HG/SS) Mud-Slap
(Pt/HG/SS) Seed Bomb
(Pt/HG/SS) Snore
(Pt/HG/SS) Synthesis
(Pt/HG/SS) ThunderPunch
(Pt/HG/SS) Uproar
(Pt/HG/SS) Zen Headbutt
(HG/SS) Headbutt
[LEFT][/LEFT]
Ludicolo -> Double Battles
->Absorb Bulb<-
Ludicolo @ Absorb Bulb / Life Orb / Lum Berry
MODEST
+Swift Swim+
4 HP / 252 SpA / 252 Spe
-Fake Out
-Hydro Pump / Scald / Surf
-Giga Drain / Grass Knot
-Ice Beam
Fake Out an undesirable opponent then proceed to get hit by Surf for paltry damage with Ludicolo's 4x Water-resistance. At that point Ludicolo will have +1 SpA and (essentially) + 2 Spd, with access to perfect coverage moves, two of which are STAB'd, one of which is also boosted by the rain. If it looks like it's possible to OHKO a foe with it, Giga Drain the HP lost from Surf back.
The choice between Hydro Pump and Scald lies in the accuracy gap, not in the Burn chance; matches played with Ludicolo are seldom matches of stall. If you choose Hydro Pump you will find that in some situations, such as against Garchomp, it will actually be wiser (if you've properly read your opponent) to use Hydro Pump, since it will hit harder than Ice Beam after a Yache Berry activates.
Lum Berry is also an option, owing to the heightened threat of a crippling Thunder Wave due to popular knowledge of Ludicolo's functionality as a Swift Swimmer.
This Ludicolo is generally used in tandem with Politoed, helping it Surf with Fake Out, but it can also switch in to another's Surf to get the boost. You may find it undesireable to have many Surf users on one team, so it may consequently be wise to use Ludicolo in one of the lead spots.