Bellsprout has a 30% chance to be found during the day, and a 20% chance to be found at night at Route 5, but only in Gold and Silver, with the same applying to Route 6. Both Bellsprout and Weepinbell can be found on Route 24, but Weepinbell is absent in Crystal in that Route, and Bellsprout is much rarer in that Route in Crystal, with the same applying to Route 25. Bellsprout can be found in Route 31 with a 30% probability, and in Route 32, they can be found with a 20% probability. They're also available to catch on Route 36, but only in Crystal. Both Bellsprout and Weepinbell can be found on Route 44, but Weepinbell is much rarer in that Route in Crystal.
A Leaf Stone may be obtained from Bill's grandfather by showing him an Oddish. Further Leaf Stones may be obtained, only in Crystal, from Picnicker Gina on Route 34, after giving her the player's number.
Lookie here! A Grass-type. In Johto. Which has a secondary evolution obtained with the use of a Leaf Stone. Okay, to be fair, the Bellsprout line in this generation is... bad. Most of the line's problems are its typing, as Grass-types and Johto aren't a great pairing. Then, there's its movepool. You know that you have a bad movepool when the only good move you get after Vine Whip is at level 24. But hey, at least during the time you get the status powders, right? Finally, one of the biggest issue in the line is the lack of accessing the final evolution during the maingame, which is by stone. Now, Crystal did kinda fix that, but you still had to wait for Picnicker Gina (the one that gives you the Leaf Stone, she's on Route 34) to call you and get yourself a Victreebel. Still, the offensive power of this line is very good, even at Weepinbell state; the problem is the lateness of the evolution and that it doesn't get as much coverage as it wishes it would, to back that up.
Gym #1 - Falkner (Violet City, Flying-type): NO. Your only attacking move is Vine Whip if you trained to level 9, and other than that, your only other option is none other than... Wrap. Which is HORRIBLE.
Gym #2 - Bugsy (Azalea Town, Bug-type): WRAP IS TERRIBLE and Scyther is really, really strong. Don't use Bellsprout here unless you want to take down the cocoons with a lot of effort and have them laugh at your sorry face in the process. ENOUGH SAID.
Rival (Azalea Town): You can easily defeat Croconaw. That's it. YOU CAN KILL ZUBAT AND BAYLEEF, THE PROBLEM IS THAT WRAP IS HORRIBLE. That, and Bayleef is very bulky, even though Razor Leaf does nearly nothing to you.
Gym #3 - Whitney (Goldenrod City, Normal-type): Don't use Bellsprout in this fight. Use Weepinbell. It 2HKOs Clefairy with the Return TM. (If you have a max friendship Weepinbell, that is. Then again, it's easy to have one.) Against Miltank? Hell no, don't use it. Set up a Sleep Powder against it, though. Victreebel, on the other hand, can defeat Miltank easily and can tank a lot of Stomps.
Rival (Burned Tower): Zubat's easy if you have Return, the same could be said for Bayleef, but the bastard takes too many hits and defeating it will not be all that fun. Croconaw is always easy, and the rest must be avoided. Unless you're using a Victreebel, in which case, all's good.
Gym #4 - Morty (Ecruteak City, Ghost-type): YOU CAN'T DAMAGE MORTY'S POKEMON FOR JACK SQUAT, DON'T USE WEEPINBELL. OR VICTREEBEL.
Eusine (Cianwood City, Crystal only): The only Pokémon you can defeat easily is Electrode. The rest must be avoided, because STAB Confusion and not being able to damage Haunter with anything other than Vine Whip are things. Victreebel can actually tank a Confusion and defeat Drowzee with Return, but not Weepinbell. Haunter, on the other hand, is basically untouchable.
Gym #5 - Chuck (Cianwood City, Fighting-type): Primeape's pretty easy: you can tank its attacks pretty well both as Weepinbell and Victreebel. Poliwrath, too. You can 4HKO it and it 4HKOs Weepinbell, but you should be able to manage with healing, unless Chuck really lucks out with DynamicPunch and confusion. That's about it, though. Even as Victreebel, you still can only 4HKO Poliwrath.
Gym #6 - Jasmine (Olivine City, Steel-type): The only Pokemon you could defeat pretty easily is... Steelix. That's it. And it hits you like a truck with Iron Tail. If you're planning to do this regardless, have fun!
Rocket Executive battle #1 (Team Rocket HQ): Weepinbell can make short work of Raticate unless it gets hit by a critical Hyper Fang, but it's a lot less risky for Victreebel. Zubat is a no-go unless you have a Victreebel with Return, and that's not the ideal option either. Koffing can boom, stay away.
Rocket Executive battle #2 (Team Rocket HQ): If you trained for Jasmine, there's no way this is hard. Murkrow might be a bit more troublesome, but not overly difficult, and you should have Acid at this point either way, which makes the fight easier. Still, don't be reckless; STAB Flying moves will hurt, and Victreebel is far from Murkrow's ideal opponent. Avoid if Weepinbell.
Gym #7 - Pryce (Mahogany Town, Ice-type): Seel's easy, Dewgong's a bit trickier regardless of your evolution stage, but Piloswine just has to be avoided because its Blizzard will wreck your face mercilessly. Pack healing items, they still all have Ice moves and Victreebel doesn't fancy them.
Rocket Executive battle #3 (Goldenrod Radio Tower): Very easy if you trained for Clair! That is, if you take out the multiple SelfDestruct Koffings... which is basically everything this team is made of. Yeah, neither Weepinbell nor Victreebel are not fit for this.
Rival (Goldenrod Underground): Haunter's a no-go, and the same goes to Magneton and Golbat. Meganium FINALLY can get some damage thanks to Acid, even better if you spent the Sludge Bomb TM on your Weepinbell/Victreebel, and Feraligatr and Sneasel should be easy too. Typhlosion? NOPE.
Rocket Executive battle #4 (Goldenrod Radio Tower): Once again, Murkrow is the one to watch out for. Arbok and Vileplume aren't that bad, but both need Return support or Weepinbell/Victreebel will be at a constant disadvantage against them, especially the unevolved form. Sludge Bomb works better for Vileplume, but Arbok resists it.
Rocket Executive battle #5 (Goldenrod Radio Tower): The Koffing is quite inoffensive since it can't explode, but neither Houndour nor Houndoom are good enemies for Weepinbell or Victreebel. Victreebel might handle the first, but that's it.
Gym #8 - Clair (Blackthorn City, Dragon-type): The Dragonairs don't dish out that much damage, except for the Ice Beam one; if you can predict which one that is, go ahead and fight the other two if you so choose. Kingdra, however, isn't an advisable fight for Victreebel, let alone Weepinbell. Once again, use Sleep Powder if you're feeling brave, because you will likely be outsped and Victreebel hates both SmokeScreen and Hyper Beam.
Rival (Victory Road): It's similar to the Goldenrod Basement battle: avoid Golbat, Typhlosion, Magneton, Haunter. And you're able to fight Sneasel, Meganium and Feraligatr.
Elite Four Will (Indigo Plateau, Psychic-type): HAHAHA NO. Weepinbell/Victreebel may be overlevelled, but it's still slow to take on much of anything, and Razor Leaf simply isn't enough even for the likes of Slowbro, due to its bulk.
Elite Four Koga (Indigo Plateau, Poison-type): Avoid fighting Venomoth, Crobat and Forretress. Ariados and Muk are easy enough, albeit really, really annoying due to evasion shenanigans. You can counter them with an X Accuracy, though, which will make all of your moves always hit in this generation, until you switch out your Pokémon. Remember that this applies to Victreebel, as Weepinbell may at best fight Ariados, but should avoid Muk.
Elite Four Bruno (Indigo Plateau, Fighting-type): Actually, this one's easy: the Hitmons can be easily dealt with Sludge Bomb, and Onix is... Onix. Can't say anything about it. Machamp's the trickier one, but Victreebel can tank its attacks fairly well. It's Weepinbell that can't, despite the resistance, due to having really bad defensive stats for this point in the game.
Elite Four Karen (Indigo Plateau, Dark-type): Umbreon is just annoying with its Sand-Attack spam, it's not too threatening at all. Vileplume and Murkrow are easy if you have patience and either Return or Sludge Bomb in Victreebel state, but Weepinbell shouldn't come anywhere close to Murkrow. Avoid fighting Gengar and Houndoom. The first one is because you can't damage it, and the second one, well... do the math.
Champion Lance (Indigo Plateau, Flying-type): Gyarados is actually... easy. Sludge Bomb can deal some pretty hefty damage to it if you're a Victreebel (avoid if Weepinbell). The Dragonites all pack a punch, and Victreebel doesn't have the right moves to fight them well. Charizard is just nope, and the same can be said about Aerodactyl.
From this point onwards, you can fight the gyms in any order, though you will need to retrieve the Machine Parts from the Cerulean City gym before you have access to the earlier portion of Kanto. Feel free to anticipate or postpone any battles as needed.
Gym #9 - Brock (Pewter City, Rock-Type): SPAM GIGA DRAIN, EVERYONE IS DEAD. At least one matchup had to be easy, right? Remember you need to beat Erika before you get the Giga Drain TM, though.
Rival (Mt. Moon, optional): Same as the Victory Road one: avoid Alakazam, Magneton, Gengar, Golbat and Typhlosion and fight the other two starters and Sneasel.
Gym #10 - Misty (Cerulean City, Water-Type): Spam Grass STAB once more and win. Again, go beat Erika first, if you don't have Razor Leaf.
Gym #11 - Lt. Surge (Vermilion City, Electric-Type): You can tank some hits, but you should avoid Magneton and the two Electrodes. They can SelfDestruct, and Victreebel hates that in the guts.
Gym #12 - Erika (Celadon City, Grass-Type): SPAM SLUDGE BOMB, EVERYONE IS DEAD. And let us reiterate how useful this gym is for Victreebel, which can finally get decent Grass STAB via Erika's Giga Drain TM.
Gym #13 - Janine (Fuchsia City, Poison-Type): Ariados is the only safe Pokémon to fight. Crobat has Wing Attack, Venomoth has Psychic, and don't even get started on the two Weezing... however, it is also worth noting that her team is very low levelled, to the point you could have something like 15 levels of advantage over her at this point. If you do, and you still have Return, then you can actually solo this gym.
Gym #14 - Sabrina (Saffron City, Psychic-Type): NOPE NOPE STAB PSYCHIC ABORT. In all seriousness, Victreebel shouldn't be your option here. If it is... then good luck, you'll need plenty.
Gym #15 - Blaine (Seafoam Islands, Fire-Type): Everyone spams Fire Blast, you dead. Don't do this.
Gym #16 - Blue (Viridian City): You can only kill Rhydon. Gyarados and Machamp might be doable, also thanks to the Fighting resistance in the latter case, but require the risk of taking hits from them and they're both physical hitters, which is something Victreebel hates. Do this only in a pinch. Avoid the rest because it has supereffective moves.
Rival (Indigo Plateau, optional): Really, nothing has changed on his team except that now he has a Crobat instead of a Golbat, and of course, that doesn't make it any more viable for Victreebel to fight against. Use the same principles and considerations as ever.
Red (Mt. Silver): Pikachu's easy, avoid Espeon and Charizard. Blastoise has Blizzard, so be careful when fighting it, and do use Giga Drain to help yourself recover some HP from its blows. Venusaur can't hurt you at all, use Return and live happily ever after. Snorlax is not really Victreebel's fight; it has bulk for days and can deal a lot of damage with Body Slam, but you can always Sleep Powder it and then leave it up to someone else.
When you get a Bellsprout, it will only ave Vine Whip in its moveset. At level 6, it learns Growth, which is... mildly useful. At level 11 Bellsprout learns Wrap... WHICH IS HORRIBLE. Then, at levels 15, 17 and 19, it learns Sleep Powder, Poison Powder and Stun Spore. All of them are useful, but Sleep Powder is the one you should get. As a Weepinbell, at level 24, it learns Acid, one of the best offensive moves that the line has to offer by level, and that's really saying something about how bad its options are. At level 33 it learns Sweet Scent, avoid it. At levels 42 and 54 it learns Razor Leaf and Slam respectively, but it's more advisable to evolve Weepinbell right after it learns Acid, unless you're pressed for Grass coverage; a level 42 Weepinbell will have a hard time getting through the challenges that Johto poses. Of course, for Gold and Silver players, there is no option B.
For TM support, this line has Sludge Bomb , Giga Drain (available only during the postgame), Return and... Cut. No shit, Sherlock. And that's it. Its TM support is pretty shallow, even moves like CUT are useful.
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.
Bellsprout Line Ratings
At what point in the game should I be evolved?: Bellsprout should be evolved right when you're near the third gym. You should use the Leaf Stone right after Weepinbell learns Acid, as it's one of the best moves it will get for a long time.
How good is the Bellsprout line in a Nuzlocke?: Sadly, not that much. Being a Grass-type line in Johto, this line isn't pretty good. But its biggest flaw in Gold and Silver is that you can't evolve into Victreebel until you arrive in Kanto, and it's in the postgame, and you need an Oddish so that you could get a Leaf Stone, so not only you're forced to wait until the postgame to evolve your Weepinbell, but you also might be able to not get the stone AT ALL due to the randomness factor of the nuzlocke challenge... unless you make a special clause that allows you to catch an Oddish just for the sake of obtaining the stone. All in all, if you're thinking about using Weepinbell, then don't do it unless you're playing Crystal: for almost half the game, it's a waste of a slot space. Victreebel could be a good choice, but don't expect too much from it.