Wurmple is found on Route 101 (40%), Route 102 (30%), Route 104 (40%), and in Petalburg Woods (25%). Cascoon is only found in Petalburg Woods (10%).
Dustox is quite a peculiar specimen. Instead of becoming a glass cannon like its counterpart, Beautifly, Dustox chooses to invest in its defenses, most notably Special Defense. However, this does not stop it from falling victim to the ‘Early Bug Syndrome’. It reaches its last evolution stage very early and will be a force in the team but will quickly peter out once you start to catch and fight stronger Pokémon. Still, this moth will not go easily into the night. With a lot of tricks, both offensively and defensively, in its repertoire and some perseverance, Dustox will be a useful member of your party. Just keep it away from bright lights and bug zappers.
Also, not so fun fact. While Beautifly quietly got a slight upgrade to its stats in Generation VI, Dustox has been left out waiting in the dark. Come on, Game Freak!
Gym #1 – Roxanne (Rustboro City, Rock-type): Dustox will not appreciate the rocks Roxanne’s Pokémon will be hurling at it. There are definitely better options, notably the starters. But if you are this desperate, you can spam Harden before targeting Geodude and Nosepass’ inferior Special Defense with Confusion. Just heal up when necessary and watch out for critical hits.
Gym #2 – Brawly (Dewford Town, Fighting-type): Here’s a Gym where Dustox can completely shine. Dustox's double resistance to Fighting STAB and access to Gust and Confusion will wash out Brawly’s Pokémon. You'd better do it quickly before any of them set up with Bulk Up and hit you hard anyway, though.
Rival (Route 110): As the Rival’s team will depend on your choice of Starter, this will be a generalized summary. Avoid the possible Slugma and Combusken. Wailmer will have Rollout so kill it before it gets the momentum going. Shroomish and Grovyle should be a piece of cake.
Wally (Mauville City): Ralts actually has no Psychic moves here, so the matchup is no problem for Dustox.
Gym #3 – Wattson (Mauville City, Electric-type): Magnemite and Magneton will completely resist Dustox and any of its STABs. Struggle Bug may be an option to lower their Special offenses but it's not advisable. Voltorb is the only thing Dustox can battle but with access to Rollout and Volt Switch, you’re better off using something else.
Tabitha/Shelly (Meteor Falls, tag battle with rival): This will be a Double Battle with one of their respective Team’s Grunts. Both Grunts will have Poison-type Pokémon -- Koffing for Team Magma and Grimer for Team Aqua -- which Psybeam will take care of quite easily. Just watch out for the Team Magma’s Koffing’s Self-Destruct. Both Shelly and Tabitha have Mightyenas, which Bug-type STAB moves will kill quickly, but their aces will differ. Shelly’s Carvanha will also fall to a Bug-type STAB, but Tabitha’s Numel should be avoided at all costs.
Tabitha/Shelly (Mt. Chimney): Shelly and Tabitha will retain their aces so the same strategies will apply. The only notable change is that their Mightyenas will be replaced by Grimer and Koffing, respectively. Deal with them with Psybeam.
Maxie/Archie (Mt. Chimney): Clearly, these teams have not heard of variety. Maxie and Archie will both have a lead Mightyena. Deal with it quickly before you succumb to confusion-hax or Roar shenanigans. They will also share a Golbat. While you can hit it hard with Psybeam, I’d suggestion switching out immediately as Golbat will outspeed you and hit you hard with Flying-type STABs. Maxie and Archie will have different aces and they will be *surprise, surprise* Camerupt and Sharpedo respectively. Sharpedo will definitely outspeed you, so be wary of its strong attacks; fortunately, it should fall fairly quickly to a Bug-type STAB. Avoid Camerupt like the plague.
Gym #4 – Flannery (Lavaridge Town, Fire-type): Don’t be ridiculous. This battle is far too sunny for this nocturnal flyer.
Gym #5 – Norman (Petalburg City, Normal-type): All of Norman’s Pokémon will be far too bulky for you to take out quickly. And with a potential 140 base power Normal STAB move targeting Dustox’s inferior Defense stat, this is not a battle you’d want to participate in.
Courtney/Matt (Southern Island, tag battle with Steven): Your first encounter with Courtney and Matt will also be a Double Battle and their Grunt will also have a Poison-type Pokémon. Second verse, same as the first: dispose of the Poison-types and Sharpedo, but avoid the Camerupt.
Tabitha/Shelly (Weather Institute): Shelly and Tabitha will only have one Pokémon: their evolved aces (Sharpedo and Camerupt, respectively). You should know what to do with them at this point.
Rival (Route 119): This is the same as the Route 110 battle, but Torchic-users should be warned of Marshtomp and its newly-learned Rock Slide.
Gym #6 – Winona (Fortree City, Flying-type): While at an obvious disadvantage, Dustox still has a chance to be successful in this battle. At this point, Dustox should have access to Toxic and Moonlight. If at a high enough level, Dustox can Toxic-stall Altaria, as the latter has no Flying STAB to abuse and Dustox is not weak to any of its attacks. Just watch out for crits as usual. Pelipper can also fall to this strategy, but it does have Aerial Ace, so be careful. Stay away from Swellow and Skarmory.
Courtney/Matt (Mt. Pyre): Courtney and Matt will have Sharpedo and Camerupt, respectively. So much for variety.
Rival (Lilycove City): The Rival will lead off with his/her new Swellow, so do not lead with Dustox. Once again, avoid the evolved Magcargo, Blaziken and Rock Slide Swampert. Wailord will also pose a threat with Water Spout and Amnesia but can fall to a set-up Dustox. Breloom and Sceptile will be no problem.
Courtney/Matt (Lilycove Hideout): Did someone say variety? No? Good, because they have the exact same "teams" as before.
Gym #7 – Tate and Liza (Mossdeep City, Psychic-type): If you are dead-set on using Dustox in this battle, then you'd better have an excellent tag team partner to carry this bout. Dustox is weak to both Lunatone and Solrock’s STABs and, despite its defenses, will not be able to take a super-effective hit, much less two in one turn. Read my mind. Do not use Dustox here.
Maxie/Archie (Seafloor Cavern): Should I even reiterate what you should do with a Mightyena? Unlike Golbat, Crobat should not be trifled with. It carries Acrobatics and is not holding an item. Enough said. Maxie’s Weezing should not be underestimated. It will have Explosion, the bane of every Nuzlocker everywhere. Dustox may not be able to deal with it quickly enough, so caution should be exercised. Archie’s Muk is another story. Only possessing Poison-type STABs, this should be a relatively easy battle. Just watch out for Screech. Although resisted, Gunk Shot will still hurt. WARNING. Both Maxie and Archie will have a Mega Stone in play. Mega Camerupt will wreck Dustox more than ever so evacuate as fast as you can. Mega Sharpedo will possibly OHKO you with STAB Crunch, so unless you’re confident you can outspeed it (you almost certainly won’t), switch out.
Primal Groudon (Cave of Origin, Omega Ruby only): NOPE. Groudon will destroy Dustox. Don’t even try.
Primal Kyogre (Cave of Origin, Alpha Sapphire only): Another NOPE for the same reason as above.
Gym #8 – Wallace (Sootopolis City, Water-type): Here’s another Gym where Dustox has the potential to shine. You can max spam Quiver Dance on Luvdisc and sweep the rest of Wallace’s team handily. Just be careful of confusion-hax from Sweet Kiss and you’ll be set.
Wally (Victory Road): Altaria will lead off Wally’s team and can hit you hard with Aerial Ace. Toxic-stall and heal up consistently if you can survive more than one Aerial Ace. If not, switch out to avoid a critical hit. Delcatty should not be a problem. You will resist Disarming Voice and Delcatty cannot hit you hard with Feint Attack, no matter how it tries. Roselia is a joke. Petal Blizzard runs off Roselia’s inferior Attack stat and is doubly resisted by Dustox. Steer clear of Leech Seed, however. Like Wattson's, Wally's Magneton will wall you and hit you hard with both its STABs. Mega Gallade should be avoided at all costs. A Psycho Cut from this Mega will definitely OHKO.
Elite Four Sidney (Evergrande City, Dark-type): It goes without saying that this bug is not afraid of the Dark. Set up with Quiver Dance and sweep the lights out of Sidney.
Elite Four Phoebe (Evergrande City, Ghost-type): Ghosts are another matter. Four out of Phoebe’s five Pokémon carry moves that Dustox is weak to: Dusclops has Future Sight, Sableye has Power Gem, the second Banette has Psychic, and Dusknoir has Fire Punch. While you can learn Shadow Ball and face these ghosts in a war of attrition, this is probably a battle best left for the experts.
Elite Four Glacia (Evergrande City, Ice-type): You will probably not be able to OHKO Glacia’s first Pokémon, Glalie, and it will most likely setup a Hail on the first turn. Continuous damage and activation of Snow Cloak for Glacia’s other Pokémon is something you do not want. It could also setup a Light Screen to reduce the effectiveness of your attacks so be warned of this. Glacia’s two Froslass will resist both of your STABs, so don’t bother with them. All in all, it’s best you leave Dustox out of the cold for this one.
Elite Four Drake (Evergrande City, Dragon-type): Barring Kingdra, all of Drake’s Pokémon pack something Dustox is weak to; and, as Dragons sometimes do, they hit hard. Toxic-stall Kingdra with a few Quiver Dances mixed in to survive, but try to avoid the rest of Drake’s Pokémon.
Champion Steven (Evergrande City, Steel-type): Unfortunately, the ultimate battle of the Pokémon League is not something Dustox can participate in handily. Right off the bat, Skarmory resists your Bug STAB, is immune to your Poison STAB, and will likely lay down Spikes on the first turn. Aggron and Armaldo will bury your bug in rocks, and even Cradily and Claydol, two of the Pokemon Dustox has a chance to beat, will carry super-effective attacks. Don’t even think about trying to use Dustox to take down Mega Metagross.
Rival (Route 103): Beware of the lead Swellow and Magcargo. Breloom will have Rock Tomb, but a Poison STAB should take care of it easily. Raichu is a new addition to the Rival’s team, but it should pose no threat to a Quiver Dancing Dustox. Ditto for Wailord. Your rival will now have a Starter with its respective Mega Stone. Now more than ever, Mega Blaziken and Mega Swampert are no-gos. Mega Sceptile will definitely outspeed and will look to crit with Night Slash or just do damage with its other attacks, but it will still be frail and will fall to two super-effective Bug Buzzes or Sludge Bombs.
Courtney/Matt (Petalburg City): Say it with me. Avoid the Camerupt, destroy the Sharpedo.
Zinnia (Granite Cave): No-go for Zinnia. All of her Pokémon will hit you hard with super-effective attacks.
Courtney/Matt (Mossdeep Space Center): Another Double Battle, same set of Pokémon. Dispose of Mightyena and Muk, but watch out for Weezing’s Explosion. Notably, Courtney and Matt will inherit the Mega Stones from their respective leaders. Mega Camerupt should be avoided while Mega Sharpedo should be trod around carefully.
Wallace (Route 131): Wallace can be dealt with the same Quiver Dance strategies, but there are some things to be aware of. Wailord will be leading off and may hit you hard with Water Spout, Earthquake, or Heavy Slam while you’re Quiver Dancing. Best not to deal with this humongous whale. You can set up, however, on either Tentacruel or Ludicolo. Only Tentacruel’s Brine can hit you for neutral damage, but as long as you remain above half health, it should not be a problem. On the other hand, Tentacruel resists both your STABs as well. If you taught your Dustox Psychic, that matchup will definitely be easier. Shield Dust will also neuter any status hax that Ludicolo is planning to inflict on you. Gyarados and Whiscash carry Rock-type attacks and should be avoided, just to be safe. Dustox can take on Milotic as long as you have set up enough Quiver Dances.
Rayquaza (Sky Pillar): NOPE.
Zinnia (Sky Pillar): Only Goodra can be battled by Dustox with Toxic-stall. Otherwise, avoid participating in this battle with the stalker.
Dustox has quite the few new tricks up its metaphorical sleeve in Generation VI ever since its debut in Generation III. As soon as it evolves at level 10, Dustox will learn Gust instead of Confusion. It will still learn Confusion early on, at level 12, so don't fret. New to Generation VI is Poison Powder at level 15, a handy status move that will be much more desired later on. Moonlight will be learned at level 17 and will be a nice form of recovery for the moth. Just be wary of any weather conditions. At level 20, Venoshock is another new toy; this is where Poison Powder will come into play. At this point in the game, a 130 base power Poison STAB will definitely wreck anything that doesn't resist it. Psybeam will come at level 22. At level 25, Dustox will learn its first natural Bug STAB in Silver Wind. While only having 5 PP and 60 base power, a 10% chance of increasing all stats is very tempting. Light Screen at level 27 and Whirlwind at level 30 could both be part of a strategy, but that particular strategy should probably be left to Pokémon who can use it better. Toxic at level 32 is definitely a key move in Dustox’s arsenal. With flawless accuracy thanks to Dustox's Poison-typing, Toxic will be useful in dealing with walls and stronger Pokémon that Dustox can switch into. Thankfully, a much needed stronger Bug STAB in the form of Bug Buzz will be learned by level 35. Protect comes in at level 37 and could be part of a successful Toxic stall. Game Freak saved the best for last. At level 40, Dustox learns Quiver Dance. Quiver Dance increases Special Attack, Special Defense, and Speed by one stage, all in one turn. All three stats are key to Dustox’s success and utility in the late game and is definitely integral to its survival.
For TMs, there are three that should be considered important for any Dustox to learn. Struggle Bug can be gotten as early as Slateport City, and it always reduces the enemy’s Special Attack by one stage. This will be useful as a nice STAB move until you get Bug Buzz and will whittle down any would-be threats. Roost is also a vast improvement on Moonlight, as Roost does not factor in weather conditions. Sludge Bomb is a powerful Poison STAB and a great move overall. Other TMs that can be used for coverage are Psychic, Shadow Ball, and Energy Ball. Giga Drain can also be taught through Move Tutors, although that's after the main game. Attract and Double Team could be also be used, if you’re feeling lucky.
Since Dustox has equal stats in Attack and Special Attack, a physical Dustox could work; but, that's not really advisable, since Dustox's physical movepool is quite barren. Return, Acrobatics and STAB U-Turn are really the only decent options it has on the physical side.
Recommended moveset: Quiver Dance + a combination of three of the following: Toxic, Bug Buzz, Sludge Bomb, Psychic, and Roost (only use Roost if you're limiting healing item use)
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.
Cascoon Line Ratings
What Nature do I want? Attack is the only stat that Dustox does not really need so any nature that does that is encouraged. Calm (-Attack, +Special Defense), Modest (-Attack, +Special Attack), and Timid (-Attack, +Speed) are the best Natures possible.
Which Ability do I want? As far as Dustox is concerned, Shield Dust is the only ability it will need. I cannot stress this enough - Compound Eyes is utterly, utterly useless on Dustox. The only move that needs Compound Eyes is Poison Powder but that will be quickly replaced by Toxic, which, by Generation VI, will always hit when used by a Poison-type. Which, guess what, is one of Dustox’s types. It is useless and a waste of an Ability slot.
At what point in the game should I be evolved? As soon as you get Wurmple/Cascoon. Cascoon does not learn any other moves naturally after Harden. Why would you want to keep it as a cocoon anyway? Wurmple and Cascoon are both absolutely useless, so it's best to take the time to grind yours up to Level 10 so that it'll actually be useful.
How good is the Cascoon line in a Nuzlocke? Honestly, Dustox is not the best Pokémon you can use in a Nuzlocke, but it’s definitely not the worst. It has good early-game presence but will definitely struggle once it faces off against other fully evolved Pokémon with higher BSTs. It can learn a lot of moves for coverage, but it will not do much with its very low offensive stats unless you've set up a few Quiver Dances. Even its defenses, which it is invested in, are not high enough allow it to survive repeated attacks with its middling HP stat. All in all, Dustox is a great option for your early-game, but it will lose its effectiveness when you start to catch better options.