Ekans can be found in the following areas: Routes 4, 8, 9, 10, 11, and 23. Arbok can be found in the following areas: Route 23 and Victory Road. They are FireRed exclusives, and cannot be obtained in LeafGreen.
Ekans and Arbok are the middle ground for all the mono Poison-types available in Kanto, yielding a significantly diverse movepool for its typing (especially in later generations). Arbok has a reputation for being relatively fast and powerful. Its Abilities either give it the edge over status effects or give it the ability to neutralize a powerful foe. They aren’t commonly seen in Nuzlockes, but they are underrated, much like other Pokémon of the Poison-type.
Rival (Cerulean City): Intimidate Ekans does pretty well here (Shed Skin Ekans doesn’t do as well but should be able to cope), being able to shut down the most powerful hitters. This works best if Bulbasaur was chosen as the starter, as Charmander is the most dangerous of the three starters your rival could have and would therefore be the most neutered by Intimidate. Intimidate can pretty much shut down Pidgeotto, which isn’t too powerful to begin with. Abra can be killed by anything that moves, as always. Hyper Fang Rattata is also heavily hindered by Intimidate, but keep in mind that a Hyper Fang crit will be pretty nasty (and it ignores the Intimidate nerf). Bulbasaur can’t do anything to Ekans except for Leech Seed, but Squirtle can pose a threat with STAB Water Gun.
Gym #2 - Misty (Cerulean City, Water-type): As long as you carry Potions, Ekans should do well, especially if it knows Bite to counter Starmie's Psychic subtyping. It’s best if you evolve Ekans before taking on Misty, though, as Arbok does much better against her than Ekans does.
Rival (S.S. Anne): Same as before, except keep away from Kadabra for obvious reasons. Dig is useful against Charmeleon, if you bothered to teach it to Arbok.
Gym #3 - Lt. Surge (Vermillion City, Electric-type): Dig is Arbok's strong point here and should allow it to OHKO Voltorb and Pikachu, but something totally not obvious that totally doesn’t live in a cave right by this city is maybe just a bit of a better Dig user.
Rival (Pokémon Tower): Don't use against Gyarados because of Thrash (unless you have Intimidate, and maybe Rock Slide to allow you to kill the Gyarados), and feel free to laugh in the face of Exeggcute with Bite or even Poison Sting. Dig is very useful against Growlithe, but might take time because of retaliatory Intimidate. Rock Slide, if you have it, is a great option to hit Growlithe, Charmeleon, Pidgeotto, and Gyarados.
Giovanni (Rocket Hideout, Ground-type): Onix and Rhyhorn can't be hit hard (except with Dig, which won’t do too much due to their high Defense stats), and Kangaskhan is a gray area, even with Intimidate, since Mega Punch hits very hard. Give Arbok a pass here.
Gym #4 - Erika (Celadon City, Grass-type): Neither good nor bad, the best option for Arbok is to attack Tangela with Bite, which targets its low Special Defense, or super-effective, STAB, haxy Poison Sting (a good move to keep thanks to the 30% poison chance). Shed Skin Arbok can reliably counter Vileplume and Victreebel as well due to the fact that it resists their attacking moves and can’t be neutered by status thanks to the 30% chance to heal status every turn with Shed Skin. Keep in mind, though, that Arbok can’t do too much back to them, since they’re immune to being poisoned by Poison Sting.
Gym #5 - Koga (Fuchsia City, Poison-type): Dig only works against Muk, so it’s best to avoid the stalemate and just keep Arbok out of this fight. Dig will take a very long time to kill Muk, allowing it to gain free turns with which to set up Double Team. Remember Ms. Hissy? Just use your Psychic-type.
Fighting Dojo (Saffron City, Fighting-type): Nothing to be careful about. You can use it here or not. You resist everything the Fighting-types in here can throw at you, but since you can’t do too much back to them, it won’t exactly be a quick, clean sweep.
Rival (Silph Co.): Same as Pokémon Tower, and you can still use Rock Slide against Charizard, Gyarados, Pidgeot, and Growlithe. Watch out for Gyarados’s Intimidate, though. Remember as well that Alakazam, at this point, has no attacking moves except for Future Sight, so feel free to use Arbok against it just for the lolz.
Giovanni (Silph Co., Ground-type): No reason to use here. You can use Dig against Nidorino and Nidoqueen if you really feel it’s necessary, as Arbok can avoid being poisoned by their Poison Point.
Gym #6 - Sabrina (Saffron City, Psychic-type): Please do not use against Sabrina, even if you have Bite. It WILL die.
Gym #7 - Blaine (Cinnabar Island, Fire-type): Dig and Rock Slide both have their uses, but only use if your Surf user (Arceus forbid) is slain or is otherwise unable to fight.
Gym #8 - Giovanni (Viridian City, Ground-type): Let me spell it out for you: A-V-O-I-D! Not convinced? How about this: E-A-R-T-H-Q-U-A-K-E. His Pokémon have it. With STAB. Yep.
Rival (Route 22, pre-Elite Four): Avoid Rhyhorn, but everything else is the same as last time.
Elite Four Lorelei (Indigo Plateau, Ice-type): Everything Lorelei has sans Slowbro is vulnerable to Rock Slide. However, keep in mind that Jynx will probably be the only one that goes down to a single Rock Slide (and even it might not). Lapras, Cloyster, and Dewgong are extremely bulky and will probably take three hits at the very least. Cloyster is honestly easier with Bite, which hits its very low Special Defense.
Elite Four Bruno (Indigo Plateau, Fighting-type): If you avoid the Onixes (they have STAB Earthquake), then Arbok can do pretty well in this fight. It resists the Fighting-type STABs of the Hitmons and Machamp, and you could hit back relatively hard with Return, Strength, Double Edge, or Earthquake. Remember that Arbok’s best weapon against these Fighting-types is simply switching in; by doing so, it lowers their damage output significantly. Also keep in mind that Machamp has Guts, so avoid poisoning it.
Elite Four Agatha (Indigo Plateau, Poison-type): Arbok is viable for almost the entire fight due to Dig/Earthquake, Rock Slide, and Bite. Take care against Haunter, though; if it puts you to sleep, use the PokéFlute immediately to avoid the incoming super-effective Dream Eater. Also watch out for her Arbok’s Intimidate. You might want to switch out after battling it to return your Attack stat to normal. Haunter and Gengar have Levitate, too, so you can’t use Ground-type moves against them. Stick with Bite.
Elite Four Lance (Indigo Plateau, Dragon-type): Useful against Gyarados (take Intimidate into account), Dragonite (watch for Outrage), and Aerodactyl (watch out for Hyper Beam) because of Rock Slide and Intimidate. Trainer discretion applies to both Dragonairs (Toxic stall might take longer due to Shed Skin).
Champion Rival (Indigo Plateau): When it comes down to it, even though you may have better coverage already, it can cover the hardest hitters on the team (Exeggutor, Charizard/Arcanine, and Gyarados). Still, Alakazam is the only actual threat to come to Arbok. Remember that Charizard, while normally going down to a single Rock Slide, can hit extremely hard with Fire Blast.
Ekans starts out with Wrap, which was only good in Generation I, and Leer, which has sucked since Generation I. At level 8, it gets Poison Sting, which is definitely worth keeping for a while, as it’s one of Ekans’ only decent moves for a while, and it has a nice 30% chance to poison opponents. Bite comes at Level 13, and will be the main move you’re going to be using for a while, along with Poison Sting. Bite has nice 60 base power which makes up for the fact that it’s specially-based in this generation and doesn’t receive STAB. It also has a great 30% flinch chance, allowing you to poison with Poison Sting and then stall out with Bite-induced flinches. Glare comes at Level 20, and while it has shaky 75% accuracy, it can be very useful if you prefer paralyzing opponents to poisoning them. Ekans doesn’t really get any good moves that Arbok doesn’t, so it’s good to evolve as early as possible (level 22). Arbok gets Screech at level 28, which isn’t a great move by any means, but it’s usable in tandem with a strong physical attack such as Strength or Dig. You’ll get Acid at level 38, which is, unfortunately, the best STAB you’ll get until the post-game. It’s better than Poison Sting, but it really doesn’t have anything over Secret Power or Strength. At level 46, Arbok will try to learn the trio of Stockpile, Swallow, and Spit Up. All of those moves suck, and to use the combination effectively, you’ll have to give up three moveslots. It’s really not worth it. Haze comes at level 56, but since the AI hardly ever sets up, there’s not much point in learning it.
As for TMs, well, Arbok learns quite a few. However, there are only a limited amount that are actually worth mentioning. Toxic is always an option, as Arbok has the potential to be a deadly staller with the combination of Toxic, Intimidate, and Bite or Rock Slide for flinchhax. Hyper Beam is also potentially useful as a finisher, but as always, it’s quite risky, especially if you’re playing on Set mode where it has lower damage output than two turns of Strength. Giga Drain is an interesting choice that allows Arbok to hit Ground/Rock types such as Graveler or Onix, but since you’re limited to one TM of that move and most Grass-types don’t learn any good moves by level-up, you may or may not want to give Giga Drain to Arbok, especially considering its mediocre Special Attack. Iron Tail can provide useful coverage against Rock-types as well, but its shaky 75% accuracy serves as a large deterrent. Plus, Steel-type coverage moves are generally unnecessary anyway. Arbok can also learn the mighty Earthquake, which is definitely a great choice if you lack any other Pokémon that would benefit more from it. Dig is a great option that you can have since early-game that can serve as a pseudo-Earthquake, but the difference in power is huge. Return is always a great move, but since you only get one TM for it, you might just want to stick with a different Normal-type move for Arbok, such as Facade or Secret Power. Rest can work well with Shed Skin, but you also need a fair bit of luck to pull off that combo. Thief is outclassed by Bite in every way, and is not worth learning. Strength is the only HM that Arbok can learn, but it’s definitely worth learning; 80 base power is quite good, especially since Arbok doesn’t get many high-powered moves.
Double Edge and Rock Slide can be learned through Move Tutors, and Arbok should be a prime candidate for Rock Slide, especially if it has Intimidate. Intimidate Arbok can switch in on nearly any Flying-type, nerf its Attack with Intimidate, and then crush it with Rock Slide. Double Edge can be a stronger alternative to Strength or Return if you need the extra power during the Elite Four, but it packs some nasty recoil.
Recommended moveset: Strength / Double Edge / Return, Earthquake / Dig, and any two between Rock Slide / Bite / Toxic / Giga Drain
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.
Ekans Line Ratings
What Nature do I want? Adamant, Brave, Naughty, and Lonely are all quite good. Modest may also seem nice, as it will raise the power of Giga Drain and Bite, but keep in mind that it’ll lower the power of your physical moves, such as Strength, Return, or Earthquake, which you will probably be using more often. Attack-lowering Natures are just plain bad, since Arbok’s Attack isn’t anything notable in the first place. A Defense-raising Nature along with Intimidate could prove handy in making Arbok a physical wall as well.
At what point in the game should I be evolved? Before Misty, ideally. You should definitely have evolved into an Arbok by the time you reach the S.S. Anne.
How good is the Ekans line in a Nuzlocke? Decent. It’s definitely nothing special, but Intimidate has the potential to be extremely useful when used correctly, and Arbok’s myriad of coverage moves allows it to take on almost any type of opponent. Its biggest drawback is that it has relatively bad stats, but it’s fun to use and is a true jack-of-all-trades, being able to act as a wall, a staller, an annoyer, or even a sweeper.
Weaknesses: Psychic, Ground
Resistances: Grass, Fighting, Poison, Bug
Neutralities: Normal, Rock, Dark, Steel, Ghost, Dragon, Fire, Flying, Ice, Water, Electric