Ludicolo is a very dangerous Pokemon to face in the rain. It has solid Special Attack, allowing it to be a fearsome sweeper. It also has very good special bulk, allowing it to take special hits very well with EV investment and annoy its opponents to no end with the “SubSeed” strategy. Even its Attack is decent, meaning it can surprise many of its counters with either Focus Punch on a special set, or by going all out with a Swords Dance set. Being able to handle almost all Water-types is not something many Pokemon can boast, so Ludicolo makes a great option for any Rain Dance team. Ludicolo can work outside of Rain Dance, usually as a SubSeeder, but it will have a harder time getting in a team slot.
Ludicolo can't cover everything in one set and so will always have problems with some Pokemon; however, with adequate support, it can get past these barriers and be a menace to your opponent's team. Its ability Swift Swim means almost no Pokemon, barring Choice Scarf users, can outspeed it, helping it sweep even more easily.
Ludicolo is an amazing special sweeper in the rain, not having trouble with the bulky Water-types that populate OU, unlike most other special Swift Swim sweepers. Surf is your main STAB attack in the rain and a truly terrifying one at that, always OHKOing the standard 248 HP / min SpD Scizor with Stealth Rock in play and hitting almost everything that doesn't resist it for at least a 2HKO. A Grass-type STAB helps deal with most bulky Water-types; the choice of Grass Knot or Energy Ball comes down to how much trouble you have with Vaporeon. If you don't have much trouble with it, Grass Knot is preferred as it hits almost all other bulky Water-types harder than Energy Ball and manages a 2HKO on bulky Gyarados, even without Stealth Rock. However, if you have a lot of trouble with Vaporeon, then Energy Ball is preferred as it still hits most bulky Water-types hard enough, but unlike Grass Knot, it does enough damage to Vaporeon so that it can't stall you out by using Wish + Protect as Life Orb recoil slowly weakens you. Ice Beam hits the Dragon- and Grass-types that resist the Water- and Grass-type combination super effectively. It also hits Flying-types super effectively, but it must be noted that a neutral Surf in the rain is stronger than a 2x super effective Ice Beam.
The last slot is the most arguable when it comes to what to use. Rain Dance is usually the preferred option as you can never have too many Pokemon with Rain Dance on a Rain Dance team, and Ludicolo has the special bulk to set it up. Focus Punch is a great alternative, though, since with a Rash nature and 60 Atk EVs, Focus Punch + Surf in the rain and Stealth Rock damage will always take out 24 HP / 232 SpD Calm Blissey, relieving Ludicolo of what is usually the biggest problem this set faces. Other useful options for this slot are Hidden Power Electric and Hidden Power Bug. Hidden Power Electric always OHKOes 4 HP versions of Gyarados, and with Stealth Rock, the same goes for bulky versions, making it particularly useful if running Energy Ball rather than Grass Knot. Hidden Power Bug has a high chance to OHKO the standard 252 HP Celebi with Stealth Rock support, whereas Ice Beam can only muster a 2HKO. When running Hidden Power Bug, use 56 HP / 252 SpA / 200 Spe since the Speed drop from running Hidden Power Bug would otherwise mean you wouldn't outrun +1 neutral natured base 100s. Hydro Pump can be used over Surf since the extra power secures OHKOs on 252 HP Togekiss, 252 HP Metagross, specially defensive Forretress, and specially defensive Skarmory for example (all with Stealth Rock support). However, the accuracy loss makes it less appealing than Surf, which still has a lot of power in the rain.Team Options & Additional Comments >>>
This sets aims to use a combination of Substitute and Leech Seed, backed by Ludicolo's solid Special Defense stat, to stall out opposing Pokemon, while also possibly supporting your team with Rain Dance or just taking advantage of opponents who use it. Substitute and Leech Seed are the main options on the set, forming the deadly combination known as “SubSeed”. A STAB attack is the best option for the third slot; Surf is a great option, especially if you're using Rain Dance or your opponent sets it up since it will gain a further 1.5x increase in power. It allows you to deal a lot of damage to Fire-types, such as Heatran, without relying on taking them out with the SubSeed combination, especially since Heatran sometimes runs Taunt, which will stop you from using the aforementioned combination. A Grass-type STAB can also be used instead to hit Water-types, especially Swampert, hard. Grass Knot hits heavier Pokemon harder, but if you prefer a harder hit on lighter Pokemon, such as Vaporeon, Energy Ball is a good replacement. Ice Beam is another option for that slot should you want to hit Dragon-types hard as well as Grass-types, which are unaffected by Leech Seed. For the last slot, Protect is the main option as it allows you to gain even more Leech Seed recovery and adds to the stalling of Substitute and Leech Seed. Toxic is another option to add to the stalling of Substitute and Leech Seed; it can actually affect most Grass-types, unlike Leech Seed, which is a bonus. Rain Dance is another option if you're using this on a Rain Dance team as this means it can set it up to support your team members and also take advantage of it.Team Options & Additional Comments >>>
Ludicolo may only have a base 70 Attack stat, but since the last thing your opponent will expect is a physical Ludicolo, this set can do some major damage. The idea is to switch into something like Swampert, who will almost certainly switch, and then Swords Dance on the switch. You may even be able to get two Swords Dances in if your opponent switches to Blissey. Waterfall is a powerful STAB attack, having 180 Base Power in the rain; it will easily OHKO Blissey after a Swords Dance in the rain, and with Stealth Rock up, 168 HP / 120 Def Snorlax always falls too. Seed Bomb is your other STAB, which hits Water-types hard, always OHKOing even the most defensive of Vaporeon at +2, and offensive Suicune too. It also does 80.2% - 95% to 252 HP / 252 Def Bold Suicune and 86.9% - 102.9% to 12 HP / 12 Def Empoleon, meaning you can sometimes OHKO them at +2 too. Ice Punch takes up the last slot to hit the Dragon- and Grass-types, which resist the Water- and Grass-type combination, hard.Team Options & Additional Comments >>>
Ludicolo could run a Choice Specs set; however, in the rain, where every rain turn is precious, this is not the best idea. ThunderPunch could be used for a powerful hit on Gyarados on the Swords Dance set; however, losing Ice Punch would make you weak to Dragon- and Grass-types, and not running Swords Dance is not an option, due to Ludicolo's low Attack stat. Seismic Toss can be used for consistent damage against everything except Ghost-types on the SubSeed set, but an attacking move such as Surf or Grass Knot is generally a better option. Giga Drain is another option for a Grass-type attack which can also recover some of your health, but the loss of Base Power makes it a much lesser option. Ludicolo could use Zen Headbutt to hit Toxicroak, but it is very rarely seen in OU. Focus Blast hits some Steel-types hard, but Surf hits most hard enough and if you want a Fighting-type attack, you're better off with Focus Punch, as that can deal with Blissey. Ludicolo can use Fake Out, but this has limited use.
Ludicolo has access to recovery in Synthesis, but it only heals 1/4 in rain so it isn't a good option. It could utilize RestTalk for some recovery, but it is better off sticking to what it does best defensively – SubSeed. Ludicolo can use Substitute to ease prediction or in combination with Focus Punch; however, this takes up a valuable moveslot, which there are better options for.
209 Speed (132 Speed EVs) should be a minimum on offensive sets to outspeed +1 positive natured Heatran in the rain. 225 Speed (196 Speed EVs) is usually best to outrun +1 neutral natured base 100s, but maxing Speed is also fine to Speed tie with other base 70 Speed Pokemon outside of rain, such as Breloom and Metagross (although they rarely run maximum Speed).
On the SubSeed set, Speed isn't important since Rain Dish is being used so focus on HP first and then Special Defense. 76 Special Attack EVs lets you OHKO most Dragonite if you're using Ice Beam after Stealth Rock damage. When running Swift Swim, more Speed would be recommended; 132 Speed EVs to outspeed +1 positive natured Heatran would be useful.
Checks and Counters
Blissey easily handles special attacking Ludicolo without Focus Punch, thanks to its enormous HP stat and high Special Defense. Snorlax similarly does very well if Ludicolo lacks Focus Punch, but needs Rest if it wants to continuously switch in. Tentacruel laughs at all sets except Swords Dance thanks to its high Special Defense and STAB Poison-type attacks to take care of Ludicolo. Unlike other special walls, it actually resists Focus Punch, which helps it counter Ludicolo even more. Celebi is 2HKOed by Ice Beam, but as long as it doesn’t switch in on that, it can handle any Ludicolo without the very rare Hidden Power Bug. Thunder Wave will make the sweeping Ludicolo sets practically useless. Cresselia can take its attacks well and effectively stop its sweep with Thunder Wave.
Most Grass-types are great counters for the SubSeed set since Leech Seed doesn’t affect them. Roserade can also take it out easily with a powerful STAB Sludge Bomb. If Ludicolo uses Energy Ball or Grass Knot, then Taunt Gliscor counters it since it can Taunt any attempts to Leech Seed and Roost off damage, while weakening it down with Earthquake or just U-turning for good damage. Abomasnow laughs at almost anything Ludicolo can throw at it, while clearing the rain. Ludicolo can Focus Punch it on the switch or 2HKO most variations with Hidden Power Bug, but these aren't used that often, especially the latter being very rare. Abomasnow's Grass-typing means it's unaffected by Leech Seed, while its high Special Defense lets it take Ludicolo's attacks well.
For the Swords Dance set, Skarmory can easily take it on by either Whirlwinding any Swords Dances it has netted or just killing it off with Brave Bird. Cresselia can wear it down with Ice Beam and sponge its hits by setting up a Reflect. Bulky Gyarados can take it on thanks to Intimidate. If it runs Bounce, it will easily OHKO Ludicolo or can just finish off a weakened one with Stone Edge. It can also cripple it with Thunder Wave. Dusknoir and Spiritomb are bulky enough to handle a Swords Danced Waterfall and can burn it with Will-O-Wisp.
Toxicroak may be UU and so rare in OU, but it can do very well since it is immune to Water-type attacks, due to its Dry Skin ability, and is also resistant to Grass-type attacks. It can also take an Ice Beam and OHKO with STAB Poison-type attacks or often with its STAB Life Orb Cross Chop, with Stealth Rock in play.