Chikorita is available as the Grass-type starter in both games.
Despite the notable buffs in terms of sheer movepool and setup options, as well as the classic annoyer/support options, Chikorita still very much struggles to find its place in Johto. The region is incredibly unkind to Grass-types, and since Meganium is one, no amount of bulk can save it from super effective moves. Much like the GSC generation, Meganium is by no means recommended to players who are looking for an easy ride - and in many ways, HGSS is not one - but it will also never disappoint those who wish for a tougher challenge, or for a dual screens user.
Rival (Cherrygrove City): Curiously, spamming Razor Leaf is the best option since it will do more damage than Tackle, because its base power and STAB make it stronger despite Cyndaquil's Grass resistance. In addition, Razor Leaf has a higher critical hit rate than Tackle. Growl should not be necessary.
Gym #1 - Falkner (Violet City, Flying-type): Chikorita can beat Pidgey with a combination of PoisonPowder and Razor Leaf. This matchup is not dangerous, as Pidgey has no Flying STAB. Pidgeotto, however, puts Chikorita - and even Bayleef, in the event of overlevelling - in serious danger, with its Gust attack, and it will restore its HP with Roost more often than Chikorita would like. There should be a better option to take down Pidgeotto.
Proton (Slowpoke Well): Chikorita is absolutely out of place in this battle. Bayleef has much better chances; it can 2HKO Zubat with Tackle (its Leech Life really does not do much) and slowly wear down Koffing with it as well. However, it is preferable to have another teammate take on Koffing, as its Smog hits about as hard as Tackle and has a high chance of poisoning. Bayleef can win the matchup on grounds of being faster, but healing items will likely be wasted on it.
Gym #2 - Bugsy (Azalea Town, Bug-type): Bayleef cannot come anywhere close to the battlefield when Scyther is on it, as a U-turn will either flat out kill it or come dangerously close. Kakuna and Metapod are harmless instead, though Kakuna could still poison Bayleef with Poison Sting.
Rival (Azalea Town): Razor Leaf disposes of Gastly in two to three hits, though beware it could use Mean Look and Curse to damage Bayleef in the process. Zubat's only super effective attack at this point is Leech Life, so go ahead and Tackle it. Quilava is Bayleef's sworn enemy and should be avoided at all costs.
Gym #3 - Whitney (Goldenrod City, Normal-type): The best strategy to use in this fight is a Swords Dance setup against Clefairy, supported by Substitute. After Bayleef reaches +6 in Attack, it can off both Clefairy and Miltank easily with Miracle Seed-boosted Razor Leaf, although Miltank will still take a hit and then go down only to the second. The Substitute helps with preventing excessive damage; even a five-hit DoubleSlap will usually deal less than 25%, making Substitute very effective. It can also prevent Bayleef from getting hit by nasty super effective moves such as Fire Blast or Blizzard, triggered by Metronome, or even worse Explosion, which is a certain kill from full health even without a critical hit. Ideally, Bayleef should still have the Substitute up and be healed - either with Synthesis or healing items - before Miltank comes into the battlefield, since Miltank will outspeed Bayleef and the Substitute, aside from preventing damage, also blocks Attract - if Bayleef is male, which is very likely - and prevents flinches induced by Stomp.
Rival (Burned Tower): Bayleef appears to have a bad matchup against everything the rival has from typings alone, but it is actually workable in this instance. Gastly cannot deal much damage directly, but it poses a very real threat with a combination of Mean Look and Curse, especially considering that Bayleef's Razor Leaf and Magical Leaf are anywhere between a 3HKO and a 4HKO; Zubat is likely to be outsped, however, and Headbutt is a 2-3HKO just like its own Wing Attack, but with the bonus flinching chance that Wing Attack lacks. Magnemite will either 3HKO or 4HKO with SonicBoom, and Magical Leaf is a 3HKO at best, so Bayleef may or may not want to fight it depending on its current HP. Quilava's Flame Wheel is too powerful; avoid it.
Gym #4 - Morty (Ecruteak City, Ghost-type): Another bad matchup all around, as all of Morty's ghosts resist Grass moves and that is all Bayleef has available to hit them. Gastly can be 3HKOed by Magical Leaf (with Miracle Seed support) before its Mean Look and Curse combo takes over Bayleef's health levels, but taking the others down will take longer than necessary, require way too many healing items, and also put Bayleef in danger against Gengar, which sports Shadow Ball. Avoid fighting them.
Eusine (Cianwood City): Drowzee will go down easily to two or three Razor Leaf attacks. Razor Leaf works best against Electrode, netting a 4HKO with Electrode's Thunder being a 5HKO at best, though Bayleef should also have Protect, as Electrode has Rollout and can become dangerous as the turns start stacking up. By comparison, its Thunder is much less scary than SonicBoom; either way, the damage it deals is fairly predictable, meaning Bayleef can stay in for as long as needed to weaken it, and then switch out to a teammate that can finish it off. Avoid Haunter since, much like the Morty fight, Bayleef cannot do much of anything to it, and Haunter can Curse-trap.
Gym #5 - Chuck (Cianwood City, Fighting-type): Bayleef has poor luck against Chuck, since both of his Pokémon can outspeed it and use Double Team or Hypnosis respectively, and Magical Leaf can only 3HKO even with the Miracle Seed equipped. While Magical Leaf is useful against Primeape, its combination of Leer and Rock Slide - which easily causes flinching - will likely make Bayleef require healing to proceed, making it liable to getting hit by a deadly Focus Punch. Poliwrath is less dangerous due to having lower Attack, but will still likely put Bayleef in trouble despite its weakness to Grass. Meganium, on the other hand, can easily solo the gym by putting up a Substitute and then hitting Primeape repeatedly with Magical Leaf, bypassing its Double Teams, then doing the same with Poliwrath. It is important that Meganium keep its Substitute up before Poliwrath comes, as Poliwrath's Hypnosis can otherwise incapacitate Meganium. Alternatively, equip a sleep-healing Berry and use Petal Dance, as Magical Leaf is still a 3HKO, although narrowly (a Special Attack-boosting nature with Miracle Seed may score the 2HKO).
Gym #6 - Jasmine (Olivine City, Steel-type): Meganium can pull off a victory with a combination of Swords Dance and Razor Leaf. However, this combination is by far sub-optimal, as it will need plenty of healing items and even at +6 Attack, Razor Leaf can OHKO the Magnemite with the Miracle Seed but is only a 2-3HKO against Steelix, which does not resist it. If the team sports better counters for these Pokémon, now is the time to use them.
Petrel (Team Rocket HQ): Strength should do fine against Zubat and Koffing which, while Poison-typed, are very underlevelled. Beware, however, that Koffing has Selfdestruct; Meganium may not want to fight it when weakneed, but a healthy one can more than take a critical hit from it. Raticate is a non-issue.
Ariana (Team Rocket HQ, tag battle with Lance): This is not the most excellent fight for Meganium to participate in, but the likely level advantage makes it workable. Arbok will be 3HKOed by Meganium's Strength, even after considering the downpowering by the hands of Intimidate, and so will Grimer; Gloom is not difficult, but can deal about a quarter with Acid. Murkrow is outright dangerous, with Wing Attack and Pursuit, though Meganium can actually withstand even a critical Pursuit on the switch if at half of its health or more. If Meganium is wounded, consider healing or switching out before Murkrow enters the battlefield.
Gym #7 - Pryce (Mahogany Town, Ice-type): A Meganium equipped with the Choice Specs and using Petal Dance can solo this fight easily, if Petal Dance strikes three times without confusing it. The Choice Specs guarantee that Petal Dance will OHKO each of Pryce's Pokémon if Meganium's Special Attack is high enough; if not, Dewgong is the only one that might survive a hit, and Meganium can take even a critical Aurora Beam from it. However, if Meganium does get confused, trying to hit Piloswine again is a major gamble; while Seel's and Dewgong's moves are not strong enough to represent an OHKO threat, Piloswine's Blizzard is if it scores a critical hit. Consider this carefully, and choose a more secure option if available.
Petrel (Goldenrod Radio Tower): Another bad matchup. All of Petrel's Pokémon have Sludge and, perhaps even worse, Selfdestruct (Koffing) or Explosion (Weezing). While Meganium's Reflect may lower damage intake from the bomb moves, it will not do any good for Sludge, and Return is the best move Meganium can use to damage Petrel's team, which only just about scratches 2HKO range against Koffing, and fails to 2HKO in the event of a lower-than-average Attack. If there are alternatives, use them.
Rival (Goldenrod Underground): Everything on this team will give Meganium a hard time, with the possible exception of Magnemite; it will be annoying to take down, but Magical Leaf or Petal Dance will eventually do the trick. Paradoxically, Sneasel and Quilava are not overly dangerous, despite having super effective moves; Quilava's Flame Wheel is only a 4HKO just like Meganium's Strength, which also has a 3HKO chance, however. Petal Dance can 2HKO Sneasel while Sneasel's Icy Wind is also a mere 4-5HKO, but if playing on Set, this will open Meganium to receiving another hit if Petal Dance continues into the third turn. Meganium should not be the one taking them on if there are better options on the team.
Proton (Goldenrod Radio Tower): At this point, Meganium might have several levels of advantage over Golbat. If this is the case, it will outspeed and 3HKO with Strength or Return. Weezing should be avoided in any case.
Ariana (Goldenrod Radio Tower): Arbok's only Poison move is Poison Sting, so Meganium should have no problems taking care of it. It can still be a long battle, though, unless Meganium manages to negate the Intimidate nerf, either through Swords Dance or switching. Vileplume has Acid, so do not try it; Murkrow has Pursuit and Wing Attack, but can be 2-3HKOed by a good Normal move (Return is almost certain to 2HKO), and Meganium can take a hit from it.
Archer (Goldenrod Radio Tower): Everything can hit Meganium for super effective damage and, while Houndour and Koffing are not too threatening by themselves, Meganium's moves will probably only damage Houndour significantly - scoring a good 2HKO in the case of Return - and Houndoom is still way outside of Meganium's league. Try using Meganium as little as possible.
Gym #8 - Clair (Blackthorn City, Dragon-type): Only one of the Dragonair has Fire Blast, which is a dangerous move against Meganium, but there is no way of knowing which. Gyarados' Dragon Rage will make Meganium need a considerable amount of healing items, but it can manage a win. In order to defeat Kingdra, however, luck will be needed, and power-ups will make it easier; if Meganium has an opportunity to set up Swords Dance and then hit with a physical move, like Strength or Return, there is a much lesser chance of a critical hit killing Meganium (which is guaranteed from full health, thanks to Kingdra's Sniper, with any move other than Hydro Pump). Substitute will also help if Meganium can keep one up; if the last move slot is still available, Light Screen is the recommended option, as it will help Meganium keep its Substitute throughout the fight until Kingdra enters. The best setup material is Gyarados, as far as Swords Dance goes: its Dragon Rage can KO only after three or more hits, and the absence of critical hits makes it very predictable. If Meganium is healed throughout, it can hit maximum Attack without a problem, and then put up a Substitute against the weaker Dragonair. Fire Blast is only a 3HKO, though it can 2HKO if it causes a burn.
Kimono Girls (Ecruteak Dance Theater): Meganium's bulk makes it a good counter for Umbreon, Espeon and Jolteon, particularly Jolteon, since Meganium resists Thunderbolt. Espeon will still be painful to fight; Psychic is very strong, and Meganium will likely only stand a chance against it if it manages to put up a Light Screen and maintain it throughout the fight; Umbreon is less of a threat, only really sporting Confuse Ray to annoy the starter. Flareon is terrifying, do not fight it. Vaporeon has Aurora Beam, but is also weak to Meganium's STAB; be careful or avoid if Meganium is weakened, but otherwise, go ahead: Aurora Beam can only 3HKO and Meganium 2HKOs cleanly with Petal Dance. Leading with Meganium against the Kimono Girls may be a good option, especially if the team has a readily available counter for Flareon, and a supplement for Espeon in case Meganium needs help defeating it.
Ho-Oh (Bell Tower, HeartGold only): Meganium would be up against a legendary with a STAB super effective move here. Do not do this.
Lugia (Whirl Islands, SoulSilver only): Meganium would be up against a legendary with a STAB super effective move here. Do not do this.
Rival (Victory Road): While Meganium is at a decisive disadvantage against all of the rival's team but his Kadabra, it can win against Magneton if it has Earthquake, and absorb some of Sneasel's hits since it still only has Icy Wind for Ice STAB. Its usage is, however, strongly discouraged against everything else.
Elite Four Will (Indigo Plateau, Psychic-type): The first Xatu has U-turn, and the second has Aerial Ace. Meganium is not ideal to fight them, but thanks to its likely level advantage, it will actually score a 2-3HKO with Return and only take up to a third in damage. Jynx's Ice Punch is also not too powerful despite the STAB, thanks to its low Attack; Meganium can take up to two hits and respond with a physical move, which will 2HKO Jynx. However, bring healing items if Meganium must fight Jynx by itself, as a Lovely Kiss lead may get Meganium into trouble if it outspeeds. Slowbro is easy pickings. Exeggutor will resist anything that is not a Normal move, so Meganium will be at a disadvantage, but it can win the matchup with some healing support.
Elite Four Koga (Indigo Plateau, Poison-type): Ariados has Poison Jab, Forretress has Explosion, Muk has Gunk Shot, Crobat has both Wing Attack and Poison Fang. Meganium can theoretically 2HKO Muk with Earthquake, taking a Gunk Shot in the process, but a critical hit will result in its death, and the rest of Koga's crew is not suitable for Meganium to battle against. Only Venomoth does not have any threatening moves, and can be taken down with Earthquake or a Normal move.
Elite Four Bruno (Indigo Plateau, Fighting-type): Meganium can set up Swords Dance to improve its fighting chances while Hitmontop is still out; combined with Substitute, this will guarantee Meganium a full +6 setup, as Hitmontop will always deal less than 25% damage unless it crits. Meganium should profit of this to max out its Attack and then put up a Substitute before killing Hitmontop, then proceed to annihilate Bruno's whole team with its strongest physical move. At +6, Body Slam and Return are sufficient to OHKO everything on Bruno's team except Onix, which is easily disposed of with a Grass move.
Elite Four Karen (Indigo Plateau, Dark-type): Meganium can get past Umbreon after breaking out of Confuse Ray shenanigans and then 3HKO Vileplume with Return, but that is it. Gengar's Destiny Bond is outright frightening and the rest has moves that hit Meganium for super effective damage, as well as potentially outspeeding.
Champion Lance (Indigo Plateau, Flying-type): Meganium does not get along with Gyarados' Ice Fang or Aerodactyl's Aerial Ace. While Aerial Ace is only a 2HKO, Meganium's moves cannot do any better than that, and Aerodactyl is also faster. Meganium also greatly suffers the matchup with Charizard and the Dragonite ace, both of which have Fire moves. One of the level 49 Dragonite also has Blizzard, whereas the other has Thunder. There is no way of telling them apart, unless their elemental attacks are baited with safer Pokémon, so unless Meganium is certain the fight is safe, it is better off not participating at all.
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): This is one of Meganium's incredibly rare chances to shine. Any Grass move will completely annihilate Brock, so go ahead and give the starter the spotlight.
Rival (Mt. Moon, optional): Meganium can still absorb Sneasel's Icy Wind well and dispose of it with Return or Earthquake; the latter also disposes of Magneton. Alakazam and Gengar have gotten significantly stronger; unless Meganium has a prior Swords Dance setup from another fight, they should be tackled with caution and a ready answer if Meganium needs to switch out, otherwise be sure to set and keep up a Light Screen at all times. Golbat and Typhlosion will both force a switch.
Gym #10 - Misty (Cerulean City, Water-type): Meganium does fairly well here. If supported by Swords Dance and either Razor Leaf or Seed Bomb, it can set up against Golduck, which will tend to Psych Up - but has no physical moves - letting Meganium sweep freely afterwards. This will, however, likely not be needed, because Golduck and Quagsire are both easily swept even without Swords Dance support while Lapras and Starmie have Ice Beam, which will do a serious number to Meganium. Meganium can set up a Substitute against either Golduck or Quagsire and defeat one of Starmie or Lapras, but not both, unless it puts its own life at risk; a critical hit from Starmie might off it, and one from Lapras means certain death.
Gym #11 - Lt. Surge (Vermilion City, Electric-type): Meganium's Electric resistance is useful, but should not be abused. Magneton is still a pain to take down unless Meganium has Earthquake, in which case it crumbles to dust in the blink of an eye. One of the Electrode can endanger Meganium with Selfdestruct, which can kill with critical hits; it also has Charge Beam, but that is the lesser problem, as Earthquake will 2HKO it for certain, or OHKO after a Swords Dance (the preferred option, as it will likely explode if left in low health from the first Earthquake). The other Electrode is not dangerous, so if the first Electrode has already been disposed of, Meganium can easily take on the second, Swords Dance or not.
Gym #12 - Erika (Celadon City, Grass-type): Jumpluff has U-turn, but its low Attack makes it a non-issue; it can be OHKOed with Return after two Swords Dances. Tangela is not threatening, but does have AncientPower, so it is preferable to set up Swords Dance against another of Erika's Pokémon. Victreebel and Bellossom, instead, only have Grass moves to hit with, so feel free to set up and sweep with Return.
Gym #13 - Janine (Fuchsia City, Poison-type): This is a Poison gym with five Pokémon knowing Poison moves, all of which are either neutral or immune to Earthquake. Even though Meganium can theoretically defeat an Ariados, they both have Poison Jab and will outdamage Meganium's Return unless it has a consistent level advantage, thus it should preferably not be used here at all.
Gym #14 - Sabrina (Saffron City, Psychic-type): Meganium is not suited to take down Espeon, due to Espeon's Calm Mind. Use a quick sweeper to dispose of Sabrina's lead, then Meganium can come in against Mr. Mime and start setting up Swords Dances for the rest of the fight. Alakazam's Psychic will hurt, but a fully healthy Meganium cannot be killed by a critical hit and two Swords Dances are sufficient to OHKO both Mr. Mime and Alakazam with a strong physical move. Alakazam also cannot kill Meganium from full health whatsoever, unless underlevelled.
Gym #15 - Blaine (Seafoam Islands, Fire-type): Meganium can easily outspeed and OHKO Magcargo with Earthquake, but should by any means stay away from Magmar and Rapidash.
Gym #16 - Blue (Viridian City): Meganium is perfect against Rhydon, and can do well against Exeggutor and Machamp with reasonable healing support; it can outdamage them after a Swords Dance and their best moves, Psychic and DynamicPunch respectively, can only 3HKO. However, neither matchup is all that easy, as Psychic can lower Meganium's Special Defense and Exeggutor also has Trick Room, whereas Machamp's No Guard will make DynamicPunch-induced confusion very annoying unless it plans on stalling out all of its DynamicPunch PPs. Gyarados has Dragon Dance and Ice Fang, whereas Arcanine has Flare Blitz; avoid them. Pidgeot's Air Slash is comparatively less threatening, but there is likely a better option on the team to fight the bird, especially as Air Slash can still 2HKO and Pidgeot outspeeds.
Rival (Indigo Plateau, optional): Meganium can KO Sneasel and Magneton with Earthquake (Return also works for Sneasel). Alakazam and Gengar have strong special moves that can also lower Special Defense, so use caution while fighting them, and preferably do so behind a Light Screen. Do not fight Crobat or Typhlosion.
Red (Mt. Silver): Pikachu should not trouble Meganium much, as its best move is Iron Tail and it cannot OHKO in any way, whereas Meganium's Earthquake does so easily. Snorlax can be very threatening with Giga Impact, but Meganium can work around it by keeping up Reflect and setting up with Swords Dance to take it down; still, be careful about Blizzard: even with Snorlax's low Special Attack, it will 3HKO just barely - specimens with a low Special Defense may even suffer a 2HKO, depending on stats - and has a relatively high chance of freezing. Likewise for Blastoise which, however, has better Special Attack as well as Blizzard; fortunately, Meganium is just fast enough to outspeed, and just powerful enough to 2HKO with Petal Dance, whilst Blastoise's Blizzard oscillates between the 2HKO and the 3HKO. Set mode players, however, will need to take into account that Petal Dance might continue into the third turn, and if Red sends out Charizard next, Meganium will be dead. Venusaur has Sludge Bomb and Charizard has STAB, both are a complete no-go.
Chikorita starts with Tackle and Growl. It then learns Razor Leaf at level 6, its strongest Grass move for a while. PoisonPowder comes at level 9, and is a nice addition to the otherwise unremarkable Razor Leaf damage in the long run, whereas Synthesis, at level 12, can be skipped if the nuzlocke rules allow to heal at will. After evolving into Bayleef, it gets Reflect at level 18. This is a very useful move, especially for the stat spread of this line, and it should be kept possibly for good. Magical Leaf comes at level 22; Bayleef can take it over Razor Leaf, unless it is either meant to run a Swords Dance set and/or its nature is Adamant, or its Attack is otherwise significantly higher than its Special Attack. Alternatively, Bayleef can keep both. Ignore Natural Gift and Sweet Scent at levels 26 and 32 respectively, they serve no purpose. Right after evolving into Meganium, at level 32, the line gets Petal Dance. This is a decisive upgrade to any other Grass move it may have, but it comes with the drawback of confusion and locking Meganium into the battle for two or three turns; choose wisely and, if possible, keep another Grass move alongside it, even if Meganium does learn Petal Dance. Meganium will re-attempt to learn Sweet Scent at level 34, so ignore it again. Take Light Screen at level 40, which paired with Reflect makes Meganium the ultimate supporter. Body Slam, at level 46, will be disposable most of the time, but it offers a good alternative to Grass moves and will usually work well on Meganium as a free "coverage" move, as most of what the line learns is either one-time-only or only rebuyable in the postgame. The last three moves are respectively Safeguard at level 54, Aromatherapy at level 60, and SolarBeam at level 66. Unless there are specific usages for them in the team, do not have Meganium learn any of these.
The most notable TM options of this line are physical, which goes hand in hand with the availability of Swords Dance. This move can be taught as early as Goldenrod City, and helps the line immensely with properly dealing damage. Sadly, apart from Return, which is available in the same city, and Strength which becomes available a little later, the only coverage Meganium gets is Earthquake, which is only shortly before the League. Still, Razor Leaf and a good Normal move are plentiful for a good chunk of the game. For Grass STAB, the best options are postgame only and come in the form of Giga Drain and Energy Ball. They are, however, better than Razor Leaf only on non-Swords Dance sets.
Meganium's pool is further widened by the Battle Frontier tutors, which can offer it Outrage and Seed Bomb on the physical side, and AncientPower on the special side. Headbutt is also a good filler move while Bayleef waits on Strength or Return.
Support: Razor Leaf / Magical Leaf / Petal Dance, Strength / Return, and any two between Swords Dance / Reflect / Light Screen
Rock-types: Rock Pokémon can cover for an overwhelming amount of Grass-type weaknesses, leaving only one uncovered, Poison. Rock STAB in general goes very well with Grass STAB, and the two most common Rock-type weaknesses are well handled by Meganium. Overall, Rock-types have the best possible synergy.
Water-types: A Water-type is always good to have on any team, even more so in the event the team also sports a Meganium. Water-types supplement Rock-types with their Fire and Ice resistance, adding further possible counters; they can also deal with dual Water/Ice-types well, which Rock-types usually do not.
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.
Chikorita Line Ratings
What Nature do I want? Meganium can work with most natures, and run physical or special sets accordingly. By contrast, its Speed will often be unneeded, even if sufficient to outrun the opponent's; as such, the best options for its nature are likely Brave, Relaxed, Quiet or Sassy.
At what point in the game should I be evolved? Chikorita should become a Bayleef before Bugsy, although either way, it will not get to contribute much to the battle. Meganium should have evolved right before Chuck, if possible, as the evolution significantly boosts its chances in the fifth gym.
How good is the Chikorita line in a Nuzlocke? Quite bad, but it is not its fault. Johto hates Grass-types to death, and the Chikorita line is no exception. It has its niche, but it will never be as good as the other two starters. It is only a recommended pick for players who are looking for a challenge.
Weaknesses: Fire, Poison, Bug, Ice, Flying
Resistances: Grass, Water, Electric, Ground
Neutralities: Dragon, Dark, Psychic, Fighting, Ghost, Rock, Normal, Steel