Poliwag can be found in Brooklet Hill and the Malie Garden in both games. In Malie Garden, it can only be found in the grass, whereas in Brooklet Hill it can be found both in the grass and the water. Poliwhirl and Poliwrath can be found in the wild, but only in Malie Garden as a SOS chain encounter under the rain at night. A Poliwhirl may be traded for a Zubat in Konikoni City.
Water Stones can be found as early as Poke Pelago's introduction after defeating Kiawe's trial, and also can be bought at Olivia's shop in Konikoni City.
Poliwrath is sadly one of the more overshadowed Water types whenever it is in the main dex. Even with Gen VI's slight stat boost, none of its stats go past the base 100 scale. It is moderately slow compared to other Water types, and its design may not entice most players.
However, one should not judge Poliwrath by its appearance. The fact that none of its stats reach the 100 benchmark means that Poliwrath's stats are more spread out evenly than most other Pokemon. Water/Fighting is a good defensive typing, taking Dark and Rock types much easier than most other Water types can hope to. Unfortunately, Poliwrath's flaws lies in its many common weaknesses and horrible movepool that does not accommodate its above-average physical stat. Before you think this frog is croaked however, Poliwrath can utilize what it has to leap ahead other choices.
Water Absorb makes it a vital defensive pivot for teams with severe water weaknesses, and can make the most of its teammates in return. Usually Poliwrath failed because it suffered from forcing you to handhold Poliwhirl to learn moves that it its evolution couldn't, but the inclusion of early TMs alleviates that pain so you can jumpstart Poliwrath from the get go.
Totem Wishiwashi (Brooklet Hill): A Damp Poliwag stands no chances against Totem Wishiwashi, which deals almost three times as much damage with Water Gun than Poliwag can do with Scald. A Water Absorb Poliwag, instead, makes the fight completely trivial, being vulnerable only to the ally Wishiwashi's Feint Attack, a weak move that takes several turns to KO. Alomomola can also hit Poliwag, though, so Poliwag should nevertheless beat Totem Wishiwashi first and the ally Wishiwashi later; Alomomola will not be called into battle if Totem Wishiwashi is over half its HP after the first turn, and then defeated before the ally Wishiwashi is.
Battle Royal (Royal Park): Poliwag's Scald can OHKO Rockruff with a good damage roll, but it is risky to use Poliwag in this battle, as the combined moves of the three enemies can take it down if one of them is a critical hit. This assumes Hau has Torracat or Brionne; if Hau's starter is Dartrix instead, the stakes are too high for Poliwag to take part in this battle.
Totem Salazzle (Wela Volcano Park): Although Scald has reasonable chances to 2HKO Totem Salazzle, Poliwag is unlikely to last more than one turn. Flame Burst is a 3HKO in spite of the resistance, and if Poliwag is poisoned, the ally Salandit - which are summoned continuously, regardless of how many are defeated - can even OHKO with Venoshock.
Totem Lurantis (Lush Jungle): The Totem's Solar Blade is overkill against Poliwag and Poliwhirl, and is not a safe option for Poliwrath especially with Trumbeak's Pluck. Avoid this one.
Plumeria (Akala Outskirts): An Eviolite Poliwhirl averagely scores a 3-4HKO against Golbat and a 1-2HKO against Salandit with Scald; Poliwrath has a problem with Golbat's Air Cutter, but it can survive due to Golbat's low Special and OHKO Salandit.
Olivia (Ruins of Life, Rock-type): This is where you should evolve Poliwhirl right now, given the easy opportunity with the stone shop. Poliwrath should rely on a water move for most of this fight, especially on Nosepass and Boldore. Nosepass may have Spark, but it's not threatening to Poliwrath. When Lycanroc comes out, you should rely on Brick Break now as its defense is not that good. Neither of Lycanroc's moves hurt Poliwrath for high damage, as they are resisted moves even with the Z-Crystal powerup.
Lana (Konikoni City, Water-type, optional): Water Absorb takes the cake here, though Chinchou should be handled with caution.
Kiawe (Royal Avenue, Fire-type, optional, Sun only): Another easy win for Poliwrath.
Mallow (Lush Jungle, Grass-type, optional, Moon only): Not the best choice, as you don't have access to Ice Beam yet.
Nihilego (Aether Paradise): Psywave is a bit of a risk to deal with, and Brick Break is not a guaranteed 2HKO even. Nihilego is likely to flee in this matchup.
Hau (Malie City): Alola Raichu is Poliwrath's worst enemy, don't even bother at all. Poliwrath can handle Flareon easily and weaken Vaporeon enough, but should not bother with Leafeon. As for the starters, the only safe one is Torracat. Brionne has Disarming Voice which is too risky at base 91 Special Attack.
Totem Vikavolt (Hokulani Observatory): Poliwrath will not be able kill either Vikavolt or its ally Charjabug quickly enough before being downed by Spark
Guzma (Malie Garden): Poliwrath resists all of Golisopod's attacks, and can kill in several hits with Body Slam. However, it must watch out for Swords Dance if it is the Damp variant. Ariados is easily picked off with Scald or Body Slam.
Totem Mimikyu (Thrifty Megamart): Poliwrath cannot hope to hit Mimikyu with either Brick Break or Body Slam, and Scald is coming off low Special Attack to a high Special Defense. Poliwrath's best chances are non-STAB Physical moves, which someone else can do better. Adding onto this, Mimikyu can OHKO with +1 Play Rough. Do not use Poliwrath here.
Plumeria (Route 15): Golbat is barely a threat if Poliwrath plays safe, and Salazzle goes down easily.
Guzma (Shady House): Poliwrath resists all of Golisopod's attacks, and can kill in several hits with Body Slam. However, it must watch out for Swords Dance if it is the Damp variant. Ariados is easily picked off with Scald or Body Slam.
Gladion (Aether House): His Golbat is much more threatening than Plumeria's, as it has an actual physical Flying STAB. No item + Acrobatics scores a 2HKO on even level, so Poliwrath should reserve its energy for the other two. Sneasel and Type: Null both go down easily to Fighting STAB.
Nanu (Malie City, Dark-type): Sableye will annoy with Fake Out and Shadow Ball, but can go down to a couple Scald or Thief attacks. Krookodile goes down easily to Scald. Persian goes down to Fighting STAB, but not in one hit thanks to Fur Coat. Poliwrath has little to fear from Dark STAB here.
Faba (Aether Paradise): Poliwrath does not want to face against STAB Psychic.
Faba (Aether Paradise, tag battle with Aether Foundation employee): Like before, everyone here has a STAB move that can take care of Poliwrath easily.
Guzma (Aether Paradise): The same as before, however Masquerain cannot be handled by Poliwrath safely as it has Intimidate and Air Slash.
Lusamine (Aether Paradise): Milotic and Bewear are the only safe matches for Poliwrath here. Lilligant definitely OHKOs with Petal Dance, and Clefable will outlast thanks to Moonblast or a surprise Metronome. Mismagius with prior setup, goes down to a Thief easily.
Hapu (Vast Poni Canyon, Ground-type): Poliwrath enjoys itself here, but should watch for its health once in a while. Work Up is the preferred move, as Scald is a better move to use on all of Hapu's Pokemon rather than Brick Break.
Totem Kommo-o (Vast Poni Canyon): The Totem cannot hope to OHKO Poliwrath at all, leaving it to set up Bulk Up easily. After that, Poliwrath is unstoppable with Brick Break.
Lusamine (Ultra Space): Same as before, Poliwrath should set up on Bewear or Milotic. However, Liligant should be cleared off the battlefield as Poliwrath has no surefire way of taking a Petal Dance.
Solgaleo (Altar of the Sunne, Sun only): Poliwrath takes all of Solgaleo's hits as mostly 4HKOS, allowing it to set up with Bulk Up and Brick Break or Thief.
Lunala (Altar of the Moone, Moon only): Lunala tanks even Thief, and OHKOs with any of its STAB.
Gladion (Mount Lanakila): Poliwrath handles Weavile and Lucario with ease, but should avoid Crobat at this point. Water and Fire Memory Silvally are easily handled, but Grass Memory should be avoided.
Hau (Mount Lanakila): Raichu is a clear avoid. Leafeon is the only Eeveeloution that can give Poliwrath a lot of trouble, so it should be avoided as well. Komala has Wood Hammer, and will hurt a lot unless Poliwrath has set up with Bulk Up. Avoid in that regard. Incineroar is a joke, however Primarina and Decidueye can take whatever Poliwrath throws at it.
Elite Four Hala (Pokémon League, Fighting-type): Most of the moves that Hala's team has, are resisted by Poliwrath. It can set up early on, and plow its way through as a result.
Elite Four Olivia (Pokémon League, Rock-type): Just like against Hala, Poliwrath can set up with Bulk Up against Relicanth, who can only put it to sleep. Poliwrath plows through, even taking Golem's Thunder Punch at +6 Defense.
Elite Four Acerola (Pokémon League, Ghost-type): Poliwrath has to be a bit more careful here, as a few Pokemon have super-effective moves to mess with it. Dhelmise, and Palossand are the most notable problems. However, Poliwrath can outspeed all and OHKO with Thief as long as it has been boosted by Bulk Up. For that reason, Poliwrath is best to set up on Sableye, Drifblim, or Froslass. Though, Sableye can break through boosts with Shadow Claw, and be generally annoying with Zen Headbutt and Confuse Ray.
Elite Four Kahili (Pokémon League, Flying-type): Poliwrath has an easy time setting up against Skarmory. However, Crobat and Oricorio will prove to be tricky as they attack on the Special side. Air Slash manages a 2HKO, coming from either Pokemon. If Poliwrath is able to survive twice, it handles Mandibuzz and Toucannon with ease, assuming it outspeeds and still has its boosts.
Professor Kukui (Pokémon League): Lycanroc can barely touch Poliwrath for anything, and goes down to Brick Break or Scald easily. Poliwrath can think about setting up again, but it encounters a roadblock on Magnezone, Ninetales, or Primarina who all attack with Special Attacks. Ninetales 2HKOs with Dazzling Gleam, but falls to a boosted Poison Jab or even Brick Break. Magnezone OHKOs with Thunderbolt, and thus should be avoided. Braviary can only be handled with prior set up. Snorlax is outlasted by Poliwrath, who 2HKOs with Brick Break. Incineroar goes down to Brick Break, and is the only safe starter kill. Poliwrath can only face Decidueye and Primarina with set up, and the assumption that it outspeeds the latter.
Poliwag starts with Water Sport, Water Gun, Hypnosis and Bubble at its earliest level. Water Sport is nice if you want to weaken fire attacks, but it's not really worth a moveslot. Hypnosis is nice to use, but be weary of that 40% miss chance. Since the Scald TM is also available in Brooklet Hill, its level-up Water STAB will be largely useless. At level 15, it learns Double Slap, which would normally be bad, but provides the only non-Water move available to the line in the beginning of the game; at level 18 comes Rain Dance, which boosts Poliwag's offensive power and is better than Water Sport at weakening fire attacks. At level 21, Body Slam is learned; this should replace Double Slap as the go-to non-STAB option, which has good base power and a good paralysis chance. At level 25 comes Bubble Beam, but due to Scald being already available, there is no use learning the move. Poliwhirl will attempt to learn it again at level 27. From this point, it is recommended that you evolve Poliwhirl which causes you to lose out on Poliwhirl's level-up moves as a result.
Regarding Poliwrath's learnset, just don't take Submission upon evolving. Brick Break is slightly weaker and has 100% accuracy, also it's not a recoil move. At level 32, Dynamic Punch is a much more powerful move, but it is highly inaccurate and not worth it as confusion got nerfed this game. Although you can keep said move if you learn Mind Reader at level 43, given they work perfectly together. Circle Throw at level 53 forces Poliwrath to go last, and may not be worth it unless you want to stop a stat-boosting Pokemon.
For Poliwhirl, it learns Mud Shot at level 32 instead. With Poliwrath's passable Special Attack, this can be used to check Electric types should you wish. Most people might save Poliwhirl so that at level 37 they can get Belly Drum, Poliwhirl's 'Smogon' move to maximize its attack. If you have the patience, go for it. Wake-Up Slap at level 43 should only be used in conjunction with Hypnosis or a partner that can sleep-status. At level 48, Hydro Pump is not worth it due to the accuracy and Scald's better utility. By level 53, Mud Bomb should not be considered as the accuracy drop isn't worth the slight power boost.
TMs are your friend, Scald and Brick Break are a must for powerful STAB choices. Bulk Up is directly before Olivia and is a great asset to boost your already good Attack and Defense stats. Though, Work Up is nice if you want a Special Attack boost too. Ice Beam is if you want to hit Grass and Dragon types hard, but keep in mind that Poliwrath's Special Attack won't be doing it any favors. Earthquake is a better option to Mud Shot, but the only coverage it grants is hitting Electric and Poison types. Psychic is a niche move to hit opposing Fighting and Poison types, but that's just it. Rock Tomb and Rock Slide are if you want to hit Flying types, but once again that is its only purpose. Rest is Poliwrath's only hardline choice for recovery, and the competitive viewpoint is to use this in conjunction with Belly Drum. Use Rest only if you're running a limited or no items campaign. Thief hits Psychic and Ghost types, and might be something you should keep temporarily. Although if you are really slow, Payback will do wonders. Poison Jab has the niche of hitting Grass types harder than Ice Beam, as well as Fairy types. This is highly recommended. Sleep Talk is, risky to use with Rest and probably should be left to Smogon. Substitute is an interesting tactic and doable, with Poliwrath's bulk. Surf hits harder than Scald, but the utility is lost. Waterfall is I repeat, Poliwrath's only physical Water move in this game. However it is post-game, so that is a serious drag.
Regarding Z-Moves, Z-Belly Drum deserves a special mention. It heals the user up before taking in Belly Drum's actual effect, making it useful for a last minute pinch. Z-Rain Dance makes it so that Poliwrath gets a speed boost, which is helpful to have. All-Out Pummeling is nice, given that Poliwrath doesn't have much strong STAB options. Though, Hydro Vortex is more useful to patch up its low Special Attack.
Fire-types: Fire types help repel Grass and Fairy attacks away for Poliwrath, who can repel Rock, Ground, and Water back in return. Lightning Rod Marowak gets a special mention. You generally should look for a Fire type that doesn't overlap weaknesses with Poliwrath.
Minimum stats are calculated with 0 EVs, IVs of 0, and a hindering nature, if applicable.
Maximum stats are calculated with 252 EVs, IVs of 31, and a helpful nature, if applicable.
What Nature do I want? Jolly is the ideal, despite lowering Special Attack which is essential for Water STAB. Other than that, Speed can also be a disposable stat if you want to keep your offense and defensive stats high. Poliwrath can even run a special set by taking away from its attack instead, should you decide to do so.
Which Ability do I want? Damp is if you plan on catching Minior, there's really nothing else for it. Water Absorb is the definite ideal, in that it adds an immunity for Poliwrath that is also its best form of recovery.
At what point in the game should I be evolved? If you don't want Belly Drum or Wake-Up Slap, then you should be evolved for the battle against Olivia.
How good is Poliwrath in a Nuzlocke? Poliwrath does decently well to tank neutral hits, and in turn can dish out strong attacks with whatever it makes the best of.