Chespin is available as the Grass-type starter in Aquacorde Town. It is given to the player by Tierno.
If "Grass starters suck" is what you are thinking, you could not be more wrong. While certainly full of weaknesses and not terribly fast, the Chespin line is quite possibly the best starter line of Kalos, and if not, it contends the first spot with Fennekin. Chespin's movepool is fairly wide even early on, and even better afterwards; its attacking power is nothing to sneeze at, and its defensive prowess is hard to rival. Chesnaught is not as straightforward to use as its Fire and Water colleagues, more on the "press this move and win" side of battling, but it is perfect for tactical play and can pull off unexpected wins against a great many Pokémon with a combination of Leech Seed, Spiky Shield and the Rocky Helmet as a held item; Chesnaught is a match made in heaven for nuzlockers who love stall and control play.
Shauna (Aquacorde Town): Go Vine Whip and then go home.
Gym #1 - Viola (Santalune City, Bug-type): Chespin has an even matchup against Surskit, but finds it hard to defeat Vivillon, due to its Infestation. Chespin can only beat Vivillon by having already used Rollout on the first turn (or more) against Surskit, and it also needs to be at half health or higher, in order to take an Infestation before OHKOing Vivillon with Rollout.
Professor Sycamore (Lumiose City): Chespin's Bite and Vine Whip can respectively defeat Bulbasaur and Squirtle easily. Charmander's Ember, however, should be avoided.
Tierno (Route 5): Two Vine Whips and Corphish will be history.
Tierno and Trevor (Route 7, tag battle with rival): Chespin should already be a Quilladin at this point. Quilladin should start off by 2HKOing Corphish with Vine Whip, and then do the same with Trevor's Pikachu and Flabébé. Chespin would still have enough bulk to defeat them all, but when the 2HKO is impossible, Corphish's Swords Dance is a dangerous move.
Gym #2 - Grant (Cyllage City, Rock-type): Quilladin can 2HKO Amaura with Vine Whip, but in so doing, it will also risk an OHKO from a critical Aurora Beam; avoid this if you have a better counter. A better matchup is the one against Tyrunt, which can be 3HKOed with Bulldoze without any significant risks.
Korrina (Geosenge Town, Fighting-type): If armed with the Rocky Helmet, Quilladin can defeat one of the Lucario with two or three Bulldoze, depending on which move(s) it uses. On average, counting the Attack boosts, Power-Up Punch will be a 3HKO starting at +0, and either a 2HKO or 3HKO (usually 3HKO, but depends on Quilladin's nature and IVs) with one turn of Swords Dance beforehand. If lucky, Quilladin may even manage to defeat both of them, but a teammate should be prepared to switch in, in case the going gets rough.
Rival (Tower of Mastery): Quilladin can 2HKO Meowstic with Shadow Claw and 3HKO Absol with Needle Arm. Holding the Eviolite, even a critical Bite will not even come close to killing Quilladin from full health. However, the matchup against Braixen is still disadvantageous, despite its only Fire STAB being Fire Spin; use another Pokémon for this.
Gym #3 - Korrina (Shalour City, Fighting-type): Mienfoo can be 2HKOed with Aerial Ace. Machoke is only a 3HKO, but once again, the Eviolite will help Quilladin take the necessary Power-Up Punches to defeat Machoke before the Attack boosts even become a problem. Quilladin should stay very far away from Hawlucha's Flying Press.
Rival (Coumarine City): Same as the Tower of Mastery matchup. Quilladin can defeat Meowstic with Shadow Claw and has an even easier time against Absol, thanks to the newfound Low Sweep TM. Braixen is still off limits for Quilladin, though.
Gym #4 - Ramos (Coumarine City, Grass-type): The most convenient evolutionary stage here depends on which of Ramos' Pokémon Quilladin or Chesnaught should take on. With the Eviolite attached, Quilladin can take Acrobatics surprisingly well, as it is a 3HKO; however, Quilladin's own Aerial Ace (or Rock Tomb) is also usually a 3HKO. In order to win this matchup, Quilladin must be healed very often, and it would still be better to pick another Pokémon for the job. Chesnaught, with its double weakness and no Eviolite boost, would not be able to dispose of Jumpluff at all. However, on the other hand, Chesnaught does significantly better than Quilladin against Weepinbell, which can still 2HKO Quilladin with Acid even with the Eviolite attached. The matchup against Gogoat is only slightly in favour of Chesnaught, because of the better offensive power; the damage taken by Quilladin from Take Down is just about the same, and Aerial Ace will still 3-4HKO Gogoat even without evolving all the way.
Aliana (Kalos Power Plant): Teach Chesnaught Low Sweep, and it will eat Mightyena for breakfast.
Gym #5 - Clemont (Lumiose City, Electric-type): Do not fight Emolga. Although Chesnaught deals more damage with Rock Tomb than Emolga does with Aerial Ace, Emolga will most likely be faster even after the Speed drop, unless Chesnaught has a Speed-boosting nature and a good Speed IV. The matchup against Magneton and Heliolisk is much better; both are 2HKOed by Low Sweep (with an OHKO chance for Heliolisk, depending on Chesnaught's Attack), and cannot do much damage to Chesnaught at all.
Rival (Route 14): Unfortunately, due to Chesnaught's newfound Fighting typing, Meowstic's Psychic now hits far too hard; avoid it. Likewise, Delphox is a bad idea; its Mystical Fire hits about as hard as Meowstic's Psychic, and both moves can OHKO on a critical hit. On the plus side, Absol is a cakewalk; waste no time using Spiky Shield or Leech Seed, however, as those moves can give it free turns to set up Swords Dance.
Gym #6 - Valerie (Laverre City, Fairy-type): Mawile can be defeated easily, as its only offensive moves are Dark-typed. Mr. Mime and Sylveon are another story; their STAB Dazzling Gleam really hurts Chesnaught, which should not attempt to fight them.
Celosia and Bryony (Poké Ball Factory, tag battle with rival): Chesnaught is an excellent choice here, due to its resistance to all moves they have minus Liepard's Slash. Liepard will not live a Low Sweep, and Manectric can be 2-3HKOed with Seed Bomb without doing much to Chesnaught in return.
Mable (Frost Cavern): Houndoom's only Fire move is Fire Fang, which cannot kill Chesnaught whatsoever. Chesnaught, on the other hand, can easily KO Houndoom with Hammer Arm.
Rival (Anistar City): Meowstic still needs to be avoided; same for Delphox. Absol is even easier than before, now that Chesnaught has access to Hammer Arm. Jolteon can easily be disposed of, with either Seed Bomb or Hammer Arm; both are 2HKOs.
Gym #7 - Olympia (Anistar City, Psychic-type): This matchup is terrible for Chesnaught, and it should never participate in this battle.
Lysandre battle #1 (Lysandre Labs): Chesnaught does poorly against Mienfoo and Murkrow, respectively due to Acrobatics and Aerial Ace, and also against Pyroar for obvious reasons. Gyarados, instead, is very easy for it: Outrage is the only move that can hit Chesnaught for neutral damage, and Spiky Shield will work very well in between turns, damaging it and speeding up the turns it takes Gyarados to be confused by repeated Outrage usage. Seed Bomb will eventually seal the KO.
Aliana (Lysandre Labs): Mightyena can be Hammer Arm'd into oblivion, and Druddigon can be walled with Spiky Shield (and a Rocky Helmet, for best chip damage output) until it drops; its Dragon Claw cannot really deal much damage.
Celosia (Lysandre Labs): Between Manectric's Flamethrower and Drapion's Poison Jab, this matchup is fairly bad all around for Chesnaught, and it should not take part in this fight.
Bryony (Lysandre Labs): Stop! Hammer Arm time!
Mable (Lysandre Labs): Houndoom's Flamethrower is far too dangerous, but Weavile's Ice Shard is actually not bad, scoring a 3HKO against Chesnaught at best; Hammer Arm OHKOs it easily.
Xerosic (Lysandre Labs): Crobat's Air Slash and Malamar's Psycho Cut only mean trouble, not counting Malamar's Contrary and Superpower combo. Use another Pokémon against Xerosic.
Lysandre battle #2 (Team Flare Secret HQ): The now-evolved Mienshao and Honchkrow are even more threatening for Chesnaught, and Pyroar remains unbeatable. Gyarados can be disposed of in the same way as the previous fight: alternate Spiky Shield with healing items and Seed Bomb, possibly with Leech Seed support, and the overgrown carp will be history.
Xerneas (Team Flare Secret HQ, X only): Xerneas is a terrible opponent for Chesnaught, which should never fight it.
Yveltal (Team Flare Secret HQ, Y only): Yveltal has STAB Oblivion Wing. Chesnaught does not even want to see it from afar.
Lysandre battle #3 (Team Flare Secret HQ): Mienshao, Honchkrow and Pyroar are still no dice for Chesnaught, but Mega Gyarados can still be fought. Its Outrage cannot kill even with critical hits, and Chesnaught will absolutely need the Rocky Helmet this time in order to fight a risk-free battle, but other than that the procedure is the same as usual: start with Leech Seed, then alternate Spiky Shield and healing or Seed Bomb, which now deals super effective damage, and Gyarados will eventually be gone. Note: for the purpose of Spiky Shield's accuracy, items do not count as "break" turns; the sequence Spiky Shield - item - Spiky Shield does not reset Spiky Shield's accuracy to 100%.
Professor Sycamore (Couriway Town): Chesnaught's matchup against Venusaur is not very favourable, but can be won if Chesnaught is temporarily retaught Return. Venusaur's only offensive moves are Petal Dance and Petal Blizzard, both harmless against Chesnaught; Return will also 2HKO Venusaur after a Bulk Up, or 3HKO otherwise. Charizard can chip away almost all of Chesnaught's health with one Flamethrower, so only a healthy Chesnaught may hope to win against it; if Chesnaught does survive, Rock Slide will OHKO. Blastoise is hopeless against Chesnaught, as its only normally effective move is the two-turn Skull Bash, which Chesnaught can easily bypass with Spiky Shield.
Shauna (Route 19): Delcatty's Play Rough and Greninja's Extrasensory are no match for Chesnaught's Hammer Arm. Only Goodra can 2HKO faster, with Sludge Wave; however, if Chesnaught opts for setting up two Bulk Ups before Goodra is sent out, it will OHKO Goodra as well. If running with healing restrictions, using Leech Seed and Spiky Shield against Delcatty is advised, to minimise Play Rough damage.
Tierno (Route 19): Talonflame's Acrobatics stomps Chesnaught flat, but Roserade and Crawdaunt are much better. Roserade's only move is Petal Dance, a mere 4HKO against Chesnaught; Chesnaught can Hammer Arm it to death easily, in two to three hits. Crawdaunt is OHKOed, as well.
Trevor (Route 19): Raichu's Thunderbolt does not do much, but it can paralyse Chesnaught with Nuzzle and even Hammer Arm is unlikely to OHKO. If Chesnaught can use Bulk Up twice before Aerodactyl comes, it will be able to OHKO it with Rock Slide or Hammer Arm; Aerodactyl's Sky Drop is a 2HKO in its normal state, and even a critical hit is unlikely to OHKO if Chesnaught's level is a little higher than Aerodactyl's (early-to-mid 50s). Florges, however, wins with Moonblast, and Chesnaught should avoid it.
Gym #8 - Wulfric (Snowbelle City, Ice-type): Chesnaught outspeeds and averagely OHKOs Abomasnow with Hammer Arm; a Chesnaught with a nature that lowers Attack may not OHKO without the Expert Belt, though, as one with a nature that lowers Speed may not outspeed (but Chesnaught can take an Ice Beam). Likewise, Chesnaught can take an Ice Beam from Cryogonal and OHKO back, but needs to be at full health for this purpose, and a critical Ice Beam will still kill it. Chesnaught should not fight Avalugg; although it hits physically, it also has Curse to boost its damage output and Chesnaught cannot defeat it in less than three hits.
Rival (Victory Road): Chesnaught cannot win against Meowstic or Delphox, but Hammer Arm OHKOs Absol and 2HKOs Jolteon. Chesnaught can also pull off a victory against Altaria through Leech Seed and Spiky Shield, as its Dazzling Gleam is a 3HKO and either Rock Slide or Stone Edge, paired with Leech Seed sapping, can get the best of the dragon bird.
Elite Four Wikstrom (Pokémon League, Ironworks Chamber, Steel-type): Chesnaught is at a decisive disadvantage against Klefki, being outsped and 2HKOed by Dazzling Gleam. However, it can defeat every other Pokémon Wikstrom has through the alternation of Leech Seed and Spiky Shield, interlaced with either Hammer Arm or Seed Bomb to deal damage. Scizor and Aegislash both only have moves that make contact, meaning they will always take damage from Spiky Shield; Aegislash also tends to alternate King's Shield with an offensive move, thus a well-timed alternation of Spiky Shield and an offensive move (after Leech Seed has been used) may even grant Chesnaught a victory without a scratch. In addition, King's Shield cannot protect Aegislash from Leech Seed. Stall is not necessary against Probopass, which can be simply KOed in two turns (due to Sturdy) with Hammer Arm.
Elite Four Malva (Pokémon League, Blazing Chamber, Fire-type): Chesnaught can survive a Flamethrower from Pyroar and OHKO back with Hammer Arm. It can also face Torkoal, whose Flame Wheel is only a 3HKO; Hammer Arm 3HKOs as well, but Chesnaught will need an Attack-boosting move such as Bulk Up or Swords Dance to win, because Torkoal can use Curse. Avoid Chandelure and Talonflame, they are unbeatable.
Elite Four Drasna (Pokémon League, Dragonmark Chamber, Dragon-type): Chesnaught can outspeed and 2HKO Dragalge with Earthquake, but Sludge Bomb is a hurtful 2HKO, which will result in a one-shot if it scores a critical hit. It fares much better against Druddigon through Leech Seed and Spiky Shield stall, as all of Druddigon's moves make contact; alternatively, it can 2HKO with Hammer Arm or Dragon Claw, but will then suffer recoil damage from Druddigon's Rough Skin. Stone Edge can 2HKO Altaria, whose Moonblast is a 3HKO, but fighting Altaria is not recommended as it can use Cotton Guard to subvert the matchup. Noivern has Air Slash, do not approach.
Elite Four Siebold (Pokémon League, Flood Chamber, Water-type): With the Expert Belt attached, Chesnaught can OHKO Clawitzer, Starmie and Barbaracle with Seed Bomb. Chesnaught can survive a non-critical Psychic from Starmie, but not a critical hit. Playing the stall game against Gyarados is not recommended: Ice Fang is a powerful move, which will 2HKO after two Dragon Dances, and OHKO at six. Only prediction play can save Chesnaught against Gyarados, and the risk is not worth taking.
Champion Diantha (Pokémon League, Radiant Chamber): Chesnaught should avoid Hawlucha's Flying Press at all costs. Tyrantrum can either be 2HKOed with good Fighting STAB (Brick Break or better) or stalled out with Leech Seed and Spiky Shield, since all of its moves minus Earthquake make contact, and it will most likely hit Chesnaught with Dragon Claw. Hammer Arm OHKOs Aurorus, but its Blizzard can OHKO back if Hammer Arm misses; Brick Break can be used instead, to stay on the safe side, and Chesnaught should be at a neutral or beneficial Speed modifier before fighting Aurorus, in order to avoid being outsped by it. A 3HKO against Gourgeist with Shadow Claw can be attempted, but its Trick-or-Treat will put a stop to it, adding a Ghost weakness to Chesnaught and turning Phantom Force from a 4-5HKO into a 2-3HKO. Chesnaught cannot win against Goodra or Mega Gardevoir, which can respectively 2HKO with Fire Blast and OHKO with Psychic.
Post-Game: AZ's Pokémon are hostile to Chesnaught with the sole exception of Golurk. Other than that, it should see its average amount of use in postgame quests.
Chespin starts with Tackle, Growl and Vine Whip. At level 8, it learns Rollout; while this move is generally dangerous to keep, and cannot benefit from the Defense Curl power boost, it may be useful in the short term, specifically against Viola. At level 11, Chespin gets Bite, a move with good base power and coverage. Leech Seed comes at level 15, and should be awarded a spot on Chespin's movepool; its physically tanky stats are likely to make a good use of it. After evolving, Quilladin will learn Pin Missile at level 20; this move is not terrible, but Bite will generally offer similar coverage and a more reliable base power. Needle Arm comes at level 26, as the very welcome and overdue upgrade of Vine Whip. Take Down, at level 30, is just not good and should be skipped; if you want a high-power Normal move, teach Quilladin Return instead. Seed Bomb comes at level 35, and is the best Grass STAB the line will learn for another twenty-something levels; hold onto it tightly. Upon evolution, at level 36, Chesnaught will learn Spiky Shield. This move is excellent, especially if paired with Leech Seed; it grants Chesnaught a great physical endurance. It should also be noted that Chesnaught learns Belly Drum and Hammer Arm at level 1, which can be remembered through the Move Reminder as soon as it becomes available. Chesnaught will also naturally learn Mud Shot at level 41, but it should be skipped, and then the much more interesting Bulk Up at level 44, good for sets that carry three offensive moves, as it makes the most of Chesnaught's bulk. Body Slam and Pain Split, at levels 48 and 52 respectively, will never really turn out useful; let them go. Wood Hammer, at level 55, has a much greater power than Seed Bomb, but at the cost of inflicting recoil damage; choose carefully whether to replace Seed Bomb or not, as Chesnaught likely has no room for two offensive Grass moves. Hammer Arm comes around again at level 60, but Chesnaught should have already learned it by now. Lastly, Giga Impact comes at level 70, also useless; Spiky Shield is also relearned at level 75, but once again, the Move Reminder exists for a reason.
Chesnaught has many TM options to choose from. Modest-natured Chesnaught may benefit from carrying Energy Ball or Grass Knot over Seed Bomb or Wood Hammer, though the physical option will generally be the go-to choice. Several Fighting moves are available before Hammer Arm, as well; Low Sweep and Power-Up Punch are good options. Brick Break would be an interesting option in general, but it gets overshadowed by Hammer Arm due to becoming available so late in the game. Bulldoze and Dig provide Ground coverage, good to deal with Electric-types until Earthquake becomes available. For Rock coverage, Chesnaught gets Rock Tomb first, and Rock Slide or Stone Edge later during the game. Shadow Claw is good against Psychic- and Ghost-types, though Chesnaught will generally not want to fight the former; Dragon Claw will help it in the matchup against Drasna, if Chesnaught gets some action. Lastly, Swords Dance is its most offensive setup option, and on the completely opposite end, Toxic is its most defensive one; it can be paired with Spiky Shield and Leech Seed to stall the enemy into oblivion.
Offensive: Swords Dance, Hammer Arm, Seed Bomb / Wood Hammer, Rock Slide / Stone Edge
Stall: Leech Seed, Spiky Shield, Seed Bomb, Hammer Arm
Rock-types: Chesnaught needs some coverage against its arch-enemies, the Flying-types of Kalos, and Rock-types are the fittest for this purpose: they usually have high Defenses, and sport a resistance to another of Chesnaught's weaknesses, Fire, as well as hitting yet another one super effectively. Although Rock-types are by no means the only ones that can help Chesnaught in this department, they have the best synergy with it.
Steel-types: Steel-types cover for even more of Chesnaught's weaknesses, totalling at five out of six, which is an astounding amount. The only downside is that they are also weak to Fire; if Chesnaught is being complemented by a Steel-type, a Water-type is also needed on the team. This is usually not an issue, as Water-types are very common and many of them are good.
Water-types: The necessary complement for the Chesnaught + Steel-type connubium, though Water-types are also useful in general on nearly any team. Water-types that aid Chesnaught and a Steel-type should preferably not add further shared weaknesses with their respective type combination; for example, Water/Rock-types are discouraged, as they would be weak to Fighting and Ground much like Steel-types are.
Fast hitters: Chesnaught's Speed is not a problem in and of itself, since Chesnaught's movepool supports its base stats very well. However, there are enemies that can set up, and Chesnaught's stall techniques will not work against them. Fast Pokémon are recommended on every team, to take on opponents against which hitting first can make or break a matchup.
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.
Chespin Line Ratings
What Nature do I want? Since Chesnaught will hardly need its Special Attack or Speed, any nature lowering either stat and boosting Attack or one of its defenses is good. Adamant and Impish are best, but natures such as Careful, Brave and Sassy are also good.
At what point in the game should I be evolved? Ideally, Chespin should be a Quilladin before the Tierno and Trevor double battle; if not there, then shortly after. Chesnaught should be fully evolved by the time Clemont is reached.
How good is the Chespin line in a Nuzlocke? Incredibly, especially for its somewhat unfortunate typing. Chesnaught has bulk, hits hard, takes special hits fairly well and can even set up with Bulk Up or Swords Dance, or simply play a slow-killing stall game with its excellent level-up moves. It needs to be used wisely, but in the hands of experienced players, Chesnaught is a highly valuable resource.
Chespin's and Quilladin's type matchups:
Weaknesses: Poison, Fire, Ice, Flying, Bug
Resistances: Ground, Water, Grass, Electric
Neutralities: Normal, Fighting, Ghost, Steel, Dragon, Psychic, Dark, Rock, Fairy