Scatterbug can be found on Route 2 by foregoing the unavoidable Pidgey or in Santalune Forest. Spewpa can also be found in the Pink Berry trees in the berry fields on Route 7.
XY's only new Bug-type line may seem like just another early game bug: a crutch character in the early game but quickly losing steam after that. However, this adorable little insect that comes in many different patterns can actually learn several interesting coverage moves. Additionally, despite its relatively low stats, Vivillon keeps itself relevant right until the end. It is statistically very frail and its common Bug/Flying typing gives it lots of weaknesses and risky matchups, but it is worth using if you get the right nature and ability. Compound Eyes Sleep Powder and availability of Quiver Dance are notable tricks up its...cocoon? Surprisingly, it can be very useful in the late game, up to and including the Elite 4.
Gym #1 - Viola (Santalune City, Bug-type): If you are fully evolved, Surskit is 2HKOd pretty easily by Struggle Bug. Viola's ace is trickier and should be avoided. Your Vivillon can use Stun Spore and a mirror match will ensue, but you won't have Infestation and your butterfly could be locked in with no way to fight back.
Professor Sycamore (Lumiose City): If you evolve, you're good against either Bulbasaur or Squirtle, but not both. Bulbasaur is easily 3HKOd with Struggle Bug, but if it gets a Leech Seed up, battling Squirtle will become risky. Squirtle is slowly whittled away at with Tackle/Return/Struggle Bug. Leave Charmander to something else.
Tierno (Route 5): Corphish hits hard, but you will outspeed it and be able to overpower it with Struggle Bug before its Swords Dances become dangerous.
Tierno and Trevor (Route 7, tag battle with rival): Vivillon is probably one of the better Pokémon to take on this battle because of how early it evolves compared to others. Nevertheless, be very careful of the opposing Pokémon ganging up on Vivillon. Pikachu is dangerous with STAB ThunderShock and Corphish becomes dangerous if given the opportunity to set up Swords Dances. Both are 2HKOd by Struggle Bug at level 16. Flabébé is relatively harmless. Your goal should be to get rid of the Corphish first and then immediately take the Pikachu out, switching or healing as necessary.
Gym #2 - Grant (Cyllage City, Rock-type): Horrible. Vivillon has low defenses and a quadruple weakness to Rock attacks, so stay FAR away.
Korrina (Geosenge Town, Fighting-type): Her two Lucario will Swords Dance and overpower you. You can stall them with Stun Spore, but you'd run the risk of them setting up before whatever unfortunate Pokémon you need to knock them out comes in. It’s best to avoid this entirely.
Rival (Tower of Mastery): At level 30, you can use Draining Kiss on Absol. Meowstic is a toss-up at best and Braixen is dangerous with Fire Spin. Stay away from both. Quilladin and Frogadier can be taken though. It’ll be slow, but it’s safe. If you have Bug Buzz, then your Vivillon is a little overleveled and can absolutely destroy Meowstic and Absol. Quilladin too, if applicable. Even Frogadier is safely 2HKOd at this level, but you’ll still have to avoid Braixen.
Gym #3 - Korrina (Shalour City, Fighting-type): You'll be able to destroy Korrina’s Mienfoo in two hits with either Draining Kiss or Psybeam. Beyond this, Vivillon is a risky choice in this gym despite the type advantage. Korrina’s Machoke packs Rock Tomb, which can OHKO Vivillon if you’re unlucky, and her Hawlucha's Flying Press deals strong neutral damage. On Shift Mode, Vivillon can avoid the Machoke and 2HKO Hawlucha with Psybeam. On Set Mode, the switches will allow Hawlucha to set up Attack boosts, so using a different Pokémon is recommended.
Rival (Coumarine City): If you have Bug Buzz it’s time to destroy. Meowstic and Frogadier may be 2HKOs, but Absol and Quilladin will go down in one hit. Without Bug Buzz, Vivillon can rely on Draining Kiss instead, but Meowstic will become tedious. Braixen is still too strong for Vivillon and should be avoided regardless of whether Bug Buzz is an option.
Gym #4 - Ramos (Coumarine City, Grass-type): This matchup is not as good as the type advantage would suggest since Ramos leads with his Jumpluff. It is much faster than Vivillon and packs STAB super-effective Acrobatics which can knock Vivillon out in one blow if it lands a critical hit. His Weepinbell can safely be 2HKOd with Bug Buzz or Psybeam but may poison Vivillon before it goes down. Gogoat’s Take Down is powerful, but Vivillon outspeeds and can 2HKO it with Bug Buzz. Only watch out for poison damage.
Aliana (Kalos Power Plant): Bug Buzz. That's it.
Gym #5 - Clemont (Lumiose City, Electric-type): No no no no no. Really bad idea. Electric owns you, Magneton also walls you, Heliolisk is strong, Emolga also has Flying moves and resists Bug, they can't be paralysed with Stun Spore, etc.
Rival (Route 14): Meowstic and Absol are destroyed by Bug Buzz. Chesnaught is now neutral to Bug Buzz, but it can’t deal major damage to Vivillon, so you can slowly whittle away its health. Meanwhile, Greninja can now be OHKOd by Bug Buzz, but will attack first with Water Shuriken, so be careful if Vivillon has already taken damage in this fight. Delphox has only become more dangerous. Avoid it completely.
Gym #6 - Valerie (Laverre City, Fairy-type): Bad. This battle is a pain for Vivillon. Mawile’s Steel typing and Mr. Mime’s and Sylveon’s high special bulk allow them to take hits for days. To make matters worse, her Mr. Mime is immune to Bug Buzz (it has Soundproof) and can set up Reflect and Light Screen, dragging the battle out even further. If you really want to, you can use Stun Spore to paralyse her Pokémon, but this is usually unnecessary.
Celosia and Bryony (Poké Ball Factory, tag battle with rival): Vivillon has a hard time taking hits from Manectric, nearly getting knocked out with a single Spark. After Manectric goes down Vivillon can Bug Buzz to OHKO Liepard just fine, although you may not want to switch in if Liepard has been able to set up with Hone Claws.
Mable (Frost Cavern): No, because Houndoom is a Fire type.
Rival (Anistar City): You should have Sleep Powder and Quiver Dance at this point, enabling a set up sweep. Neither Meowstic can deal significant damage to Vivillon, so cleanly setting up is possible if your rival doesn’t switch. At +5, Vivillon can OHKO every single potential Pokémon on your rival’s team except Flareon. Flareon is 2HKOd, but should be avoided because is can OHKO Vivillon with a crit Lava Plume.
Gym #7 - Olympia (Anistar City, Psychic-type): Another surprisingly bad matchup. Sigilyph’s Air Slash and Magic Guard and Slowking’s Power Gem (so many random Pokémon have Power Gem in this game) make them opponents that should be avoided. Meowstic is easily beaten with Bug Buzz though, you can prevent it getting too many Calm Minds in with Sleep Powder.
Lysandre battle #1 (Lysandre Labs): Mienfoo dies immediately to Hurricane, but be very careful of Acrobatics, which knocks off over half of Vivillon’s health. Pyroar is an absolute no with Fire Blast, Gyarados is too tanky and strong to consider, and Murkrow is frail but risky to take on thanks to Aerial Ace. If you can get in a set up in on Mienfoo, then great, but don't count on it too much.
Aliana (Lysandre Labs): Bug Buzz is fine for Mightyena, but Druddigon is too strong. If you have Sleep Powder and Quiver Dance, you can set up on Mightyena and take them both down. Mightyena can prevent the sweep with Taunt if you don’t put it to sleep first. Bug Buzz OHKOs Druddigon at +4. You can do it with Hurricane at +3, but that has a chance of missing.
Celosia (Lysandre Labs): Manectric is even worse than last time, packing Thunderbolt. Drapion doesn't take much damage from Bug Buzz or Hurricane. You can use Sleep Powder to make this fight easier for other team members, but it can miss even with Compound Eyes.
Bryony (Lysandre Labs): Bug Buzz works wonderfully against Liepard, but Bisharp’s Iron Head and Night Slash are too strong; put it to sleep or don't fight it. You can set up on Liepard with Sleep Powder and Quiver Dance if it doesn’t use Taunt.
Mable (Lysandre Labs): No. Everything has moves that are too strong and/or super effective against Vivillon.
Xerosic (Lysandre Labs): Crobat is a horrible match up because it carries Air Slash. Malamar instantly dies to 4x effective Bug Buzz. The only problem is finding an opportunity to switch Vivillon in. Be very careful of crit Psycho Cuts or switch in on a predicted Superpower. Vivillon afford not to care about the stat boosts since it will target Malamar with special attacks.
Lysandre battle #2 (Team Flare Secret HQ): This is a really bad matchup for Vivillon. Lysandre’s Mienshao can now outspeed Vivillon and OHKO with Acrobatics. Honchkrow’s Aerial Ace is also much more dangerous and should now be avoided. Pyroar and Gyarados are just as bad as last time and Vivillon should stay away from this fight entirely.
Xerneas (Team Flare Secret HQ, X only): Xerneas wrecks you with superior stats and powerful moves. You could try Quiver Dance to tank special attacks from it, but it's not recommended. Sleep Powder might help to catch it, but that’s it.
Yveltal (Team Flare Secret HQ, Y only): Yveltal is even worse than Xerneas. It's a particularly painful with encounter with Oblivion Wing and should not be attempted.
Lysandre battle #3 (Team Flare Secret HQ): It’s the same bad matchup as before except that Mega Gyarados becomes a Dark type. It is super bulky and will likely tank a Bug Buzz, then respond with Ice Fang, which will do major damage if not OHKO Vivillon. Since Mienshao outspeeds Vivillon, you will probably not be able to set up the boosts you’ll need to take down any of these Pokémon.
Professor Sycamore (Couriway Town): You might be slightly overleveled after the Lysandre fights. Venusaur only has Grass-type moves. This is a great opportunity to set up Quiver Dances, but watch Vivillon’s health since you can’t put Venusaur to sleep with Sleep Powder. At +4, Vivillon can OHKO all three with Hurricane. Watch out for misses since Charizard can knock Vivillon out with a Flamethrower.
Shauna (Route 19): If you use Delcatty to set up Quiver Dances to a ridiculous extent, you'll win. You will need Sleep Powder and healing items. Delcatty’s Return can deal over half of Vivillon’s health in damage. If you don’t set up, Goodra will wall Vivillon and eventually overpower it. With the starters, the same as always follows: avoid Delphox (unless you’ve been able to set up to +4 to OHKO with Hurricane or +5 to OHKO with Bug Buzz), while Greninja and Chesnaught can be beaten with Bug Buzz and Hurricane respectively.
Tierno (Route 19): Don't fight Talonflame at all. Swords Dance, Acrobatics, and higher speed are all major issues for Vivillon. Roserade only uses Petal Dance, so Vivillon can take advantage of the quadruple resistance and blow it away with Hurricane. Crawdaunt is weak to Bug Buzz and should be OHKOed, but be very wary of switching in on Set Mode because of Vivillon's low Defense. Night Slash and Crabhammer both take off over half of Vivillon's health and Crabhammer can OHKO from full health with a crit.
Trevor (Route 19): Trevor will beat Vivillon easily. Raichu and Aerodactyl have the natural type advantage with Electric and Rock moves respectively while Florges walls special attacks without prior set up. Setting up on Florges is tedious since it carries Confide, but technically possible if you really want/need to do it.
Gym #8 - Wulfric (Snowbelle City, Ice-type): Bad, of course, due to type match ups. Abomasnow is weak to both Flying and Bug, but carries Ice Shard, which will 2HKO Vivillon before you can 2HKO it. Avalugg’s low Special Defense is not low enough for you to kill it before it kills you. Cryogonal will both wall you and kill you.
Rival (Victory Road): Setting up Quiver Dances against Meowstic to nuke everything is the best option. This allows you to power through Altaria, Jolteon, Flareon, and Delphox. If you don't set up, these Pokémon will beat you easily with their super-effective moves. Absol, Meowstic, Greninja and Chesnaught lose to your STABs while Vaporeon can be taken if you are careful of Aurora Beam, and/or have set up enough Dances beforehand to not care.
Elite Four Wikstrom (Pokémon League, Ironworks Chamber, Steel-type): You could probably actually set up against Klefki and beat everything else other than Probopass. Watch Vivillon’s health and put Klefki to sleep first, since it has a chance to 2HKO Vivillon with either Dazzling Gleam or Flash Cannon. This will also make setting up easier since it packs Torment too. Keep in mind that Aegislash cannot be OHKOd by Hurricane at +6 and deals massive damage with Iron Head. Put it to sleep first before attempting to kill it. Avoid Probopass. It has Sturdy to survive any hit and will use STAB Power Gem to beat you.
Elite Four Malva (Pokémon League, Blazing Chamber, Fire-type): Take a guess :P
Elite Four Drasna (Pokémon League, Dragonmark Chamber, Dragon-type): Not good. All four of her Pokémon can beat you easily. Vivillon naturally outspeeds all of Drasna’s Pokémon except Noivern, so you could use them to set up Quiver Dances, but this is very risky. Dragalge can OHKO an unlucky Vivillon with a critical hit Thunderbolt if it wakes up early. Druddigon can deal massive damage with a boosted Retaliate or waste your set up with Dragon Tail. Altaria is the safest setup fodder of the three once you put it to sleep. Just make sure it doesn’t put Vivillon to sleep with Sing first. If you’ve been able to set up to +3, you can attempt Noivern. Keep in mind that Hurricane can miss, and Noivern’s Air Slash will definitely kill Vivillon if it does.
Elite Four Siebold (Pokémon League, Flood Chamber, Water-type): If you get in a Sleep Powder and set up to +6 on Clawitzer, you'll be fine. This is slightly risky, since Vivillon is OHKOd by a crit Water Pulse because of Clawitzer’s Mega Launcher. Starmie is easier to set up on since it doesn’t hit as hard, but carries Light Screen to make Vivillon’s job harder and typically comes in after Siebold’s Gyarados. Do not attempt Gyarados or Barbaracle if Vivillon hasn’t been able to set up. Gyarados carries Dragon Dance and may become difficult for any of your pokemon to kill. Barbaracle carries Stone Edge.
Champion Diantha (Pokémon League, Radiant Chamber): Diantha’s Hawlucha makes ideal setup fodder, to the point you might be able to solo her entire team after enough Quiver Dances. Kill Hawlucha immediately if it sets up more than one Swords Dance though. If you don't set up to +6, you're only likely to beat Hawlucha and Gourgeist with Hurricane. Besides, there is no good time to switch Vivillon in on Tyrantrum (with Head Smash) or Aurorus (with Blizzard), so it’s the best opportunity to get Vivillon into the fight. At +6, Vivillon comfortably OHKOs every Pokémon except Goodra, which is a possible 2HKO and has a chance to OHKO Vivillon with Fire Blast. You can’t use Sleep Powder because it has Sap Sipper, so make sure your Vivillon has a minimum Special Attack stat of 147 or carries a Sharp Beak to guarantee the OHKO.
AZ (Credits): If only he didn’t lead with Torkoal. That thing carries Stone Edge unfortunately, so don’t lead with Vivillon. Golurk is easier, you can 2HKO it with Hurricane. Be careful of misses as always, Phantom Force is no joke, 2HKOing Vivillon. Thank goodness it’s a two-turn move and Golurk is slower than Vivillon. Sigilyph has Air Slash and Cosmic Power, and you have no way to OHKO it unless you’ve set up on Golurk with Quiver Dance. A +3 Bug Buzz will kill Sigilyph, but avoid it if you haven’t set up.
Scatterbug comes with the generic Tackle and String Shot. At level 6, it learns Stun Spore, setting it apart from other early Bugs such as Caterpie. On evolving into Spewpa at level 9, it gets Protect... yeah. It’s not a bad move, but this Bug seldom has move slots to spare. At level 12 it evolves into Vivillon and get Struggle Bug, which will be your main Bug STAB for the first third of the game. With the ability to hit multiple opponents and lower their Special Attack, it's pretty good. It gets Psybeam at level 17, which is really good coverage against Fighting-types until Vivillon learns a good Flying STAB move. Level 25's Draining Kiss following that is quite weak but can heal Vivillon and increase its longevity. At level 35, it gets Bug Buzz, the best special Bug move in the game. It’s a powerful STAB and comes relatively early. At level 45, Quiver Dance comes along. It is one of the best set up moves for Vivillon, giving it necessary Speed and Special Attack boosts, and is what keeps it relevant late game. At level 50, you finally get a Flying STAB. It's Hurricane, which is insanely powerful and 91% accurate with Compound Eyes. These last three moves dramatically increase Vivillon's potency. At level 55 you get the unique Powder for use against Fire-types, but it's not recommended.
The Move Reminder's best gift is Sleep Powder, which Vivillon won't learn again by level, unlike Butterfree. Compound Eyes boosts the accuracy too. As for TMs, you get Infestation, which is interesting but not very useful in the late game. Psychic and Energy Ball are fun, but typically do not hit as hard as Vivillon’s STABs and are unnecessary in the late game. Hyper Beam is good for the fun factor but typically very risky. There are a lot of other interesting moves like U-Turn, and Acrobatics, but they use Vivillon’s weaker offensive stat and are not recommended. You could run a troll set with Substitute and Double Team if you really want to.
Rock-type Pokémon: This type covers for 2 of Vivillon's 5 weaknesses, and fortunately, these are the 2 most common ones. Vivillon thrives alongside a Rock-type Pokémon because this typing resists Flying and Fire type moves. Most Rock types also have the defenses necessary to take neutral hits that Vivillon cannot. In return, Vivillon can typically be switched in on Fighting, Ground and Grass type moves and handles Pokémon with lower Special Defense than Defense.
Bulky Water-type Pokémon: While most Water-types share a common Electric weakness with Vivillon, they make up for it by covering Vivillon's true weakness: an inability to take hits. Water STAB attacks are super-effective on Fire and Rock, two of Vivillon's worst weaknesses. They also resist Ice and Fire attacks. Many Water-types also learn Ice-type coverage moves, allowing them to take care of Vivillon's Flying weakness too. As a bonus, Rain Dance will give Vivillon's Hurricane a 100% chance of hitting and reduce the damage dealt by Fire-type attacks.
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.
Scatterbug Line Ratings
What Nature do I want? You definitely want a Speed or Special Attack increasing nature as Vivillon's stats are only modest (which, coincidentally, is a useful nature). Modest and Timid are good since they lower Vivillon’s least useful stat. Avoid natures that lower Speed and Special Attack. Natures that lower Vivillon’s defensive stats are not terrible, but should be used with caution since Vivillon lacks the bulk to shake off hits.
Which Ability do I want? You really, really want Compound Eyes for Hurricane and Sleep Powder to be more accurate than usual, as these traits are integral to Vivillon's success and it not dying because it missed the opponent. Fortunately, Scatterbug and Vivillon have exactly the same two abilities (with Spewpa temporarily replacing them with Shed Skin) so you'll know instantly if you've got the right ability. Shield Dust isn't that great.
At what point in the game should I be evolved? You'll want to evolve immediately for Struggle Bug. There’s no need to delay the evolution unless you’re trying physical Vivillon for some reason. In that case, wait until level 15 for Bug Bite, then evolve to Spewpa.
How good is the Scatterbug line in a Nuzlocke? It can be incredibly difficult to use, but it continues to get new moves at the right times to keep itself relevant. It does suffer from quite a few bad matchups, but can set up and sweep on many ordinary trainers, as well as take out Calem/Serena's Pokémon depending on what you pick. You have to play smart and anticipate coverage moves, especially from Fighting types. It is very fragile, but it is definitely less impressive on paper than in action, and it may just surprise you. It is a lot more potent than other early Bugs such as Butterfree or Beedrill, but it lacks Sleep Powder until the Move Reminder, which gives Butterfree the advantage. Later on, Quiver Dance and Hurricane obliterate several Pokémon that posed threats earlier.