Froakie is available as the Water-type starter in Aquacorde Town. It is given to the player by Tierno.
The very star of the Gen VI Super Smash Bros is likely the most known Kalos starter ever, and its usefulness nearly outlives its own fame. With Greninja's Water-typing, which is excellent defensively even with its mediocre-to-balanced defensive stats, and the incredibly many TM moves it has access to, the line is easily one of the few that really do not need to try hard to find a spot on the team, even more so thanks to its starter status. Even some of the very early TMs in the game can be learned and proficiently used by Frogadier, and getting to Greninja status opens up an even wider range of choices.
Nevertheless, despite the versatility, Greninja is not as overpowered as it is with Protean as its ability, and while it may be one of the starters with the highest number of favourable matchups in the region, it is by no means miles better than its two alternatives. As it is a Water-type and a jack of all trades, it will hardly be a master of any of them, and the other Water-type options will offer it competition in the long run; still, as a consolidated team member by then, Greninja is highly unlikely to ever be useless in any given team, or to fall short in raw offensive power.
Gym #1 - Viola (Santalune City, Bug-type): Froakie's Quick Attack outdamages Surskit's, winning it the matchup easily. Winning the matchup against Vivillon is much more difficult: while its Infestation deals low damage, and is largely problematic due to the residual HP chipped away every turn, Froakie's Bubble is outdamaged by Vivillon's Tackle. It will be much simpler for Froakie to win if it already knows Water Pulse, which 3-4HKOs Vivillon.
Professor Sycamore (Lumiose City): Froakie must avoid Bulbasaur, which 2-3HKOs with Vine Whip. Charmander is easily defeated by Bubble, or Water Pulse if Froakie already knows the move; Squirtle may give Froakie more problems due to Tail Whip and Withdraw, but Bubble still deals as much damage as a Quick Attack at +2 (Squirtle's) Defense and Water Pulse outdamages it after a single Withdraw, so Froakie can still win.
Tierno (Route 5): Corphish has Swords Dance and a physical move, Vice Grip. It is better taken care of by something with powerful, neutral STAB, as it could become dangerous in the long run. An already evolved Frogadier, instead, 2-3HKOs it with Water Pulse despite Corphish's Water resistance.
Tierno and Trevor (Route 7, tag battle with rival): Frogadier's Water Pulse is an average 2HKO against Pikachu and 2-3HKO against Flabébé, which is just about sufficient for Frogadier to target Pikachu first, in hopes of taking it down before it strikes with a second Thunder Shock. Frogadier can take up to two, but Flabébé knows Vine Whip, as well, which can pile up in damage with Pikachu's STAB. Unless overlevelled, Frogadier should preferably not fight against Corphish, as it would easily be subject to Swords Dance and Vice Grip.
Gym #2 - Grant (Cyllage City, Rock-type): Amaura can be 2HKOed with Water Pulse, and Frogadier can take up to three Refrigerate-boosted Take Downs, in the event that Amaura chooses to lead with Thunder Wave and Frogadier is unable to attack for some turns. Tyrunt wins the matchup against Frogadier, as both of them 3HKO (Tyrunt does so with Rock Tomb), but Frogadier will eventually be outsped. Winning against Tyrunt is possible only if Frogadier is healed once.
Korrina (Geosenge Town, Fighting-type): Frogadier's Water Pulse 3HKOs both of the Lucario at best, which is very bad, because they can 3HKO with Power-Up Punch, or even by using Swords Dance once and then Power-Up Punch twice, an even worse case scenario which leaves them at +4 Attack before Frogadier goes down. A better suited Pokémon should be used here.
Rival (Tower of Mastery): An Eviolite Frogadier can stand Meowstic's Psybeam well, and respond with Thief, which averagely 3-4HKOs; Water Pulse is also guaranteed to 3HKO Absol, whose Bite can do no better, and Absol is also slower than Frogadier. Quilladin must be avoided, as its Needle Arm is too strong.
Gym #3 - Korrina (Shalour City, Fighting-type): Frogadier's Aerial Ace scores a good 2HKO against Mienfoo and a 3HKO against Machoke; both of them will not have enough time on stage to use Power-Up Punch enough to become threatening. However, Hawlucha's Flying Press is stronger than any of Frogadier's moves even if Frogadier holds the Eviolite, and Hawlucha also has two other moves that boost its Attack; do not fight Korrina's ace with Frogadier.
Rival (Coumarine City): It is recommended to run the Eviolite in this fight. While Acrobatics may be tempting to use, especially against the rival's Quilladin, the 2HKO is not guaranteed and Needle Arm takes away a sizeable chunk of Frogadier's health. With the Eviolite, instead, Frogadier can take on Meowstic with Thief like it did in the previous matchup, and also 3HKO Absol with Water Pulse.
Gym #4 - Ramos (Coumarine City, Grass-type): A Frogadier with no held item and Acrobatics is capable of defeating both Jumpluff and Weepinbell, 2HKOing them; whether or not Frogadier will need healing in the process, however, depends on whether it can outspeed Jumpluff or not, as its Acrobatics combined with Weepinbell's Grass Knot are a potential KO. Gogoat's Grass Knot is too strong for Frogadier, but Greninja circumvents the issue by 2HKOing it with Acrobatics if its health is still high.
Aliana (Kalos Power Plant): Surf is an average 2HKO against Mightyena, or 3HKO in the worst case scenario. The only possible element of disruption is Mightyena's Swagger, which can be circumvented by healing confusion or switching out.
Gym #5 - Clemont (Lumiose City, Electric-type): Greninja is too fast to score a KO in this battle; Emolga will likely Volt Switch out of the battlefield after Greninja's leading Surf, and both Magneton and Heliolisk have high chances of OHKOing it with Thunderbolt. The ninja frog should be kept on the sidelines for this battle.
Rival (Route 14): Greninja's STAB Thief can now 2HKO Meowstic, and its Dark resistance improves its matchup against Absol as well, which is 2HKOed by Surf anyway; however, if Meowstic has used Light Screen prior to engaging in the fight against Absol, Greninja should 3HKO with Acrobatics instead, because Surf would be outdamaged by it. Slash 3-4HKOs naturally, so even a combination of Slash and Swords Dance will not help Absol win against Greninja. Chesnaught should preferably be avoided, because Acrobatics just barely fails to OHKO and Chesnaught's Seed Bomb can do so.
Gym #6 - Valerie (Laverre City, Fairy-type): Mawile's only offensive moves are Dark-typed, which means it can be knocked out easily with Surf. Mr. Mime is 2HKOed by Poison Jab, regardless of whether it uses Reflect or not; Dazzling Gleam can only OHKO if it scores a critical hit. Sylveon should not be fought, as it easily outpowers Greninja.
Celosia and Bryony (Poké Ball Factory, tag battle with rival): While Manectric's best STAB move is Spark, Greninja still suffers from the weakness and a low base Defense, which amount to Spark 2HKOing. Dig can 2HKO Manectric, but the move is very risky to use, as the turn spent underground can help the opponents KO the rival's Meowstic and then gang up on Greninja. Overall, the starter should preferably enter the battlefield only after Manectric is defeated; it can deal with Liepard easily with either Surf or Acrobatics, thanks to its resistance to Liepard's Assurance.
Mable (Frost Cavern): Piece of cake. Surf's up!
Rival (Anistar City): Meowstic can now be likely OHKOed by Dark Pulse, if Greninja is holding the Expert Belt; Absol is still 2HKOed by Surf. Greninja also resists both of Vaporeon's good moves, Muddy Water and Aurora Beam, and can wear it down with Dark Pulse, which is an average 4HKO against it. Once again, it should preferably avoid Chesnaught; even though an Expert Belt-boosted Acrobatics still 2HKOs despite having only 55 BP, Chesnaught's OHKO chance with Seed Bomb persists.
Gym #7 - Olympia (Anistar City, Psychic-type): Sigilyph can be OHKOed with Expert Belt-boosted Dark Pulse; this combination guarantees Greninja a relatively worry-free battle afterwards, as Sigilyph would otherwise likely set up either Reflect or Light Screen. Slowking is 2HKOed with Dark Pulse or Night Slash, regardless of its possible Calm Mind usage; Meowstic is also 2HKOed by both moves, Dark Pulse having a small OHKO chance, once again only with the Expert Belt attached. As the only move Meowstic can use to deal damage to Greninja is Shadow Ball, even multiple Calm Minds will not threaten it, in the event that Slowking used Yawn and put Greninja to sleep.
Lysandre battle #1 (Lysandre Labs): Greninja will be OHKOed by Mienfoo's High Jump Kick if it attempts to fight it; Acrobatics is not powerful enough to OHKO it. Instead, it can 2HKO Murkrow and OHKO Pyroar with Surf. It must not fight Gyarados, either, whose Outrage is almost twice as strong as Greninja's Dark Pulse.
Aliana (Lysandre Labs): Mightyena is easily 2HKOed by Surf. Druddigon can theoretically be 3HKOed with Dark Pulse, but Greninja will be at a considerable risk in the event that the first Dark Pulse does not score the flinch; Druddigon's Dragon Claw is highly likely to 2HKO.
Celosia (Lysandre Labs): Manectric's Thunderbolt has a very low chance to OHKO, and Greninja's Surf can 2HKO; while risky, the matchup is winnable. Drapion, instead, flatly 2HKOs with X-Scissor without a chance for Greninja to do any better.
Bryony (Lysandre Labs): Liepard is 2HKOed by Surf, but Bisharp 2HKOs Greninja with X-Scissor. A better counter is needed to fight Bisharp.
Mable (Lysandre Labs): Houndoom is OHKOed by Surf with Expert Belt support; Weavile can 3HKO with Low Sweep and is only 3HKOed by Surf, which has a far too low chance to 2HKO to matter, so Greninja must eventually switch out against it.
Xerosic (Lysandre Labs): Greninja's Extrasensory is guaranteed to 2HKO Crobat if backed by the Expert Belt, though if Crobat outspeeds, its X-Scissor is a possible - but not guaranteed - 2HKO against Greninja. Malamar is Greninja's sworn enemy, sporting a super effective Superpower with Contrary as its ability; Greninja should come nowhere close to it.
Lysandre battle #2 (Team Flare Secret HQ): Although Extrasensory has a relatively high chance of OHKOing Mienshao, it should not be fought, as its High Jump Kick will kill Greninja; gambling with Protect may result in Mienshao using Swords Dance, which is even worse. Greninja can 2HKO Honchkrow with Surf, however, and OHKO Pyroar with Surf; it needs the Expert Belt to guarantee both. Greninja must also still avoid Gyarados, which outpowers it by far.
Xerneas (Team Flare Secret HQ, X only): Moonblast and Fairy Aura. If Greninja does so much as enter the battlefield, it will be dead.
Yveltal (Team Flare Secret HQ, Y only): Yveltal's Oblivion Wing is a 2HKO against Greninja, and restores a sizeable chunk of Yveltal's health in the process. Greninja should not be used against it.
Lysandre battle #3 (Team Flare Secret HQ): Greninja must still avoid Mienshao, as it is far more likely to die to its High Jump Kick than kill it with Extrasensory. Surf disposes of Honchkrow in two hits, and Pyroar in one, providing Greninja holds the Expert Belt. The now-Mega Gyarados has a newly acquired weakness to Grass, as well as a higher weight, so Greninja can 2HKO it with Grass Knot.
Professor Sycamore (Couriway Town): Venusaur's Petal Dance one-shots Greninja and Acrobatics cannot OHKO it; Charizard is easily OHKOed by Surf instead, if Greninja holds the Expert Belt. Blastoise can be 3HKOed with Dark Pulse, or even 2HKOed by Grass Knot, which prevents it from executing Skull Bash altogether.
Shauna (Route 19): Delcatty's low Attack makes Play Rough effectively much less dangerous than it may sound, scoring a mere 3HKO against Greninja's 2HKO Surf. The most effective way to beat Goodra is Night Slash, which hits its lower defensive stat and 3HKOs; if not with Night Slash, Greninja would be unable to prevail without healing, as Goodra's Dragon Pulse also 3HKOs. Delphox is 1-2HKOed by either Surf or Night Slash.
Tierno (Route 19): Talonflame is no match for Greninja's Surf, but Roserade's Petal Dance OHKOs Greninja and Acrobatics is very likely, but not guaranteed, to OHKO it; Greninja should U-turn to a Pokémon with a Grass resistance instead, since Petal Dance is the only move Roserade knows. Crawdaunt is 2HKOed by Grass Knot.
Trevor (Route 19): Greninja is highly likely to OHKO Raichu with Expert Belt-boosted Dig, and Raichu's Thunderbolt cannot kill Greninja from full health, unless a critical hit is scored. Aerodactyl is OHKOed by Surf. Florges straight up murders Greninja with Moonblast, and should not be fought under any circumstance.
Gym #8 - Wulfric (Snowbelle City, Ice-type): Abomasnow's Energy Ball is not an OHKO, thus Greninja can 2HKO it with Poison Jab instead, if the Expert Belt is held; alternatively, Acrobatics without the Expert Belt will do the same. Cryogonal is also 2HKOed with both combinations, and its moves cannot inflict significant damage on Greninja; however, its Confuse Ray can get in the way of sweeping. Greninja also deals with Avalugg swiftly, 2HKOing with Surf.
Rival (Victory Road): Dark Pulse backed by the Expert Belt has a high chance of OHKOing Meowstic, and can also once again 4HKO Vaporeon, whose moves have not changed and are still all resisted by Greninja, save for the weak Quick Attack. Altaria is OHKOed by Ice Beam, assuming Expert Belt; Surf 2HKOs Absol, as usual. Chesnaught is better off fought by another Pokémon, as its Seed Bomb is still likely to OHKO and Acrobatics cannot do the same.
Elite Four Wikstrom (Pokémon League, Ironworks Chamber, Steel-type): Klefki can be 2HKOed with Surf before it does so with Dazzling Gleam, though its Torment will foil that plan. Probopass is 2HKOed as well, and its Discharge is relatively non-threatening, only reaching 3HKO range. Scizor has a low OHKO chance with X-Scissor, and can be 2HKOed with Surf, but taking this risk is not worth it if it can be helped. Greninja can beat Wikstrom's Aegislash, too, by either 2HKOing Aegislash-Shield with Dark Pulse, or OHKOing Aegislash-Blade with the same move, though it needs every last bit of its HP to be certain to survive Aegislash-Blade's Sacred Sword.
Elite Four Malva (Pokémon League, Blazing Chamber, Fire-type): An Expert Belt Greninja scores a series of easy OHKOs against Malva with Surf.
Elite Four Drasna (Pokémon League, Dragonmark Chamber, Dragon-type): Greninja can 2HKO Dragalge with either Ice Beam or Dig, as well as the Expert Belt. Ice Beam also easily OHKOs Altaria and Noivern, but Druddigon is only 2HKOed, and its Revenge can kill Greninja in one blow after the first Ice Beam; although the chance is small, no chances should be taken if another Druddigon counter is available.
Elite Four Siebold (Pokémon League, Flood Chamber, Water-type): Greninja should fight Clawitzer only if no other options are available, as its Aura Sphere comes close to OHKOing and even the Expert Belt cannot guarantee that Grass Knot will score a 2HKO; Gyarados would use Greninja as Dragon Dance fodder, and is thus even more dangerous than Clawitzer. Instead, Greninja can OHKO Starmie safely with Dark Pulse, assuming Expert Belt support; if not, Dark Pulse is a 2HKO at best, but Greninja can also take a Dazzling Gleam. Grass Knot OHKOs Barbaracle as well.
Champion Diantha (Pokémon League, Radiant Chamber): Greninja outspeeds and 2HKOs Hawlucha with Ice Beam and the Expert Belt, and can take a Flying Press from it. Though the move can also 2HKO Tyrantrum, with a small OHKO chance, Tyrantrum's Head Smash is also a 2HKO but unlikely OHKO; if Tyrantrum can be taken on in a safer manner, Greninja should not risk it. Aurorus is marginally safer, as it can be 2HKOed with Surf even if it uses Light Screen, and a healthy Greninja survives a Thunder from it, unless a critical hit is scored. The Expert Belt also allows Greninja to OHKO Gourgeist with Dark Pulse. Goodra is 3HKOed by Ice Beam, but its Dragon Pulse has a small chance to 2HKO; once again, Greninja should be used only if there are no safer options available. Lastly, Mega Gardevoir is overkill against Greninja, which should never come close to it.
Post-Game: The AZ fight is not hard, and the Looker Bureau episodes should not spell danger for Greninja either, except for Malamar's Superpower. Greninja will likely see some use in this segment, if you decide to nuzlocke further.
Froakie starts off with Pound, Growl, and Bubble. The buff received by Bubble makes it more than viable for the beginning of the game, and Pound will serve its purpose against Water-types. At level 8, it learns Quick Attack, a nice priority upgrade over Pound, although with Froakie's Speed it will rarely matter; Lick comes at level 10, and it's moderately useful for catching, not being a powerful move. The first remarkable upgrade comes at level 14, with Water Pulse; this move is excellent for a good while in the game, having a respectable BP of 60 before STAB and the confusion chance. After evolution, Frogadier learns Smokescreen at 20, which is not really all that useful; however, Round at level 23 will provide a much better alternative to Quick Attack for anything that resists Water. Fling comes at level 28, but should just be ignored. Then, Smack Down at 33 can be considered, but it is very likely Frogadier will have better alternatives at that point in the game - last but not least, Rock Tomb. Right after evolution, Greninja learns Water Shuriken at 36; this move can be useful for physically-oriented starters, but is more often than not outclassed by Water Pulse, and Surf when it becomes available, plus Greninja is so fast that it will hardly ever need priority. It then gets Substitute at 43, which will very likely not be useful at all, given Greninja's not so good defenses; Extrasensory, at 49, provides a neat coverage boost instead, especially for Dark monolockers who are looking for a response to Fighting-types. Double Team comes at 52, but is a fairly irrelevant move, and available via TM earlier than that; Haze comes at 56, and may situationally be considered if Greninja must fight enemies that can set up, though it will usually not find a spot on Greninja's overbooked moveslots. Hydro Pump comes at level 60, and can be preferred over Surf for higher power, but at the cost of a lower accuracy. Night Slash is the only Dark-type STAB it gets by level without Heart Scales, and should definitely be kept; it is, however, better relearned as soon as the player reaches Dendemille Town, as it's also a level 1 move for Greninja. Lastly, at level 75, Water Shuriken comes round again.
There is an unbelievably vast selection of TMs Greninja can learn; it will always be hurting for more than four moveslots. As with any Water-type, Ice Beam or Blizzard is a must, especially if the team in its whole provides no answer to Dragon-types; Greninja's STAB of choice can be either Surf or Waterfall, depending on which attacking stat is higher. The other STAB can be obtained in the form of Thief even before evolution, then Night Slash from the move tutor, and even Dark Pulse later on, for specially-oriented ninja frogs. Dig is a great middle-game move and provides coverage against Electric-types, but Greninja will hopefully not need to fight any. Aerial Ace works similarly for Fighting- and Grass-types, and can also be upgraded to Acrobatics in Coumarine City, for the moderate price of not letting Greninja hold an item. Rock Slide also provides great coverage, U-turn is best on Set mode when switches can be necessary at any given point, and Grass Knot complements its Water STAB well, but will also overlap with a good number of Water matchups, therefore only being useful situationally.
Recommended moveset: Surf / Waterfall, Night Slash / Dark Pulse, Ice Beam, U-turn / Acrobatics / Grass Knot
Poison-types: Greninja's two STABs are very useful, but they also open up a fairly wide attack surface. Fortunately, four of its five weaknesses are very well covered by Poison-types, which resist them all and can also deal super effective damage to the common Grass- and Fairy-types. There is no other type that covers Greninja's weaknesses so well, and without adding a redundant weakness on the team; Poison-types are a must have as Greninja's companions.
Ground- or Dragon-types: The only one of Greninja's weaknesses left uncovered by Poison-types is the Electric weakness. Electric-types with Lightning Rod can perform a defensive role, but usually do not have the necessary coverage to hit back; Ground- and Dragon-types are preferred for this job.
Physical tanks: Greninja's special bulk is acceptable, but its physical bulk is quite lacking. Having a dedicated physical wall should be standard on any team, even more so if Greninja is a member of it.
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.
Froakie Line Ratings
What Nature do I want? Greninja's versatility will make it work essentially with any nature. Whatever boosts Special Attack will go well with its special movepool, and whatever boosts Attack will go well with its physical movepool. Neutral natures work both ways, as do natures that only affect defenses and/or Speed. Greninja's Speed is also high enough to not suffer from any potential nature nerfing.
At what point in the game should I be evolved? Froakie should become a Frogadier at Parfum Palace or thereabouts, for better in-battle rendition, and either way definitely before the Grant battle. It should then be a Greninja before Clemont, though in that specific battle, evolution will not matter as much as it otherwise would, due to Clemont's type speciality.
How good is the Froakie line in a Nuzlocke? Very versatile, as its hidden ability would suggest, and generally finds a good niche in just about any team, thanks to its starter status and very varied movepool. If the team needs a more specialised Water-type role, however, there will likely be better suited Pokémon to use; this is one of Greninja's weak points: being a jack of all trades, it is also master of none.