Tangela can only be encountered with all areas of the Great Marsh. It is most common in areas 3 and 4, as a relatively common encounter during the day, and slightly less common at night. In all other areas it is a rare encounter.
Tangrowth is an interesting Pokémon, fitting of its different manner of evolution. Fittingly, its arsenal of moves is also special for a Grass-type, packing access to Electric, Flying, Rock, Ground, Poison and Fighting cover atop its STAB moves and Normal coverage. Boasting high stats outside of its iffy speed and special defense, this mass of blue spaghetti will provide a solid alternative to those looking for a bulky Grass-type and did not take Turtwig at the start of the run.
Gym #4 - Maylene (Veilstone City, Fighting-type): Tangela and Tangrowth's high physical defense shines here, letting either stage of the line soak up the entire physical focus of the gym while slowly whittling her Pokémon down with Mega Drain and Sleep Powder. Tangrowth is probably better suited overall due to its higher overall bulk making crits easier to manage as well as its access to Focus Blast to destroy Lucario with.
Rival (Pastoria City): Staravia and his Fire-type is too much for Tangela to deal with if it has not evolved prior to this fight. Tangrowth however, has plenty of options to handle most of his team. Shock Wave allows you to bypass his Staravia's Double Team and Endeavor into Quick Attack combo without issue while Aerial Ace cuts through Monferno, Roselia and Grotle with ease. Prinplup and Buizel are easy targets and while you have enough bulk to ignore Ponyta's Embers, your best option here is Focus Blast.
Gym #5 - Crasher Wake (Pastoria City, Water-type): Quagsire drops to your STAB move of choice while Gyarados gets zapped into submission through Shock Wave. Floatzel is somewhat dangerous through Ice Fang, but its fragility versus Tangrowth's bulk should allow your spaghetti monster to come out on top.
Cyrus (Celestic Town): Sneasel can only 3HKO a level 39 Tangrowth through Ice Punch while it gets OHKO'd in retaliation through Brick Break or Focus Blast. Golbat's Air Cutter is also only a 3HKO in contrast to Shock Wave being a 2HKO. Just be careful of crits. Murkrow is in the same boat, have at it.
Rival (Canalave City): If you started with Piplup, Barry's only managing a 3HKO on Tangrowth (0 Atk Infernape Flame Wheel vs. 0 HP / 0 Def Tangrowth: 48-56 (34.5 - 40.2%) and 0 Atk Staraptor Aerial Ace vs. 0 HP / 0 Def Tangrowth: 48-56 (34.5 - 40.2%) -- guaranteed 3HKO ) and if you began with any other starter, Tangrowth will resist most attacks, with the exception of Staraptor's moves and Fire Spin. As such, while healing will be needed frequently, mainly against Infernape and Staraptor, this entire team should not present too much of a problem for Tangrowth.
Gym #6 - Byron (Canalave City, Steel-type): Earthquake is a clean OHKO on Magneton, although Flash Cannon is getting close to being a 2HKO, so a crit will sting. Focus Blast OHKOs Steelix and its Ice Fang is merely a 5HKO, so even with the questionable hitrate of Focus Blast, you win. It's also how you OHKO Bastidon at equal levels to avoid being countered to death by Metal Burst against Earthquake.
Saturn (Lake Valor): You outdamage Golbat with Shock Wave, scoring a likely 2HKO in comparison to its certain 3HKO with Air Cutter. Be ready to pop a Hyper Potion and Tangrowth will win here. Bronzor is a pain in the rear, packing Levitate to be immune to Earthquake and a neutrality or resistance to everything Tangrowth has besides a Fire-typed Natural Gift, which is a 2HKO. Thankfully Focus Blast is able to do about 45-55% per hit at level 42, although a Pokémon with an actual Fire-type move is recommended. Toxicroak can only 3HKO with Poison Jab; however Tangrowth needs Earthquake in order to deal with it faster, and a critical hit with of Poison Jab will turn it into a near OHKO which can be catastrophic if it poisons.
Mars (Lake Verity): Her Golbat is literally a carbon copy of Saturn's, so the same points apply. The same applies to her Bronzor, although this one knows Confuse Ray, which may be an annoyance. Purugly is at most doing 28% to a level 42 Tangrowth between Fake Out and Slash, while Focus Blast is a clean OHKO. Just pack a Chesto Berry to combat Hypnosis.
Gym #7 - Candice (Snowpoint City, Ice-type): While the type-disadvantage may seem unappealing, Tangrowth is able to ensnare Sneasel without issue, being 5HKO'd at worst by Ice Shard while either of your Pokémon's Fighting-type options are certain OHKOs. Piloswine is similar given that it can only 2HKO with full power Avalanches. While Tangrowth is only working with a chance to OHKO with Focus Blast, with Giga Drain being a 2HKO, it only needs 63 speed in order to certainly outpace Piloswine, letting it safely take it out. Abomasnow and Froslass are too dangerous due to being faster, chip damage from hail and high attacking stats backing up their STAB-powered Ice-type moves.
Cyrus (Galactic HQ): Sneasel has the same issues that it had last time, only able to 3HKO with Ice Punch before getting flattened by Tangrowth's Fighting move of choice. Crobat shares a 3HKO between Air Cutter and Shock Wave, the difference being that Tangrowth will never outspeed it, stay away. The same applies to Honchkrow, which outspeeds and 2HKOs with Drill Peck.
Saturn (Galactic HQ): You outdamage Golbat with Shock Wave, scoring a likely 2HKO in comparison to its certain 3HKO with Air Cutter. Be ready to pop a Hyper Potion and Tangrowth will win here. Bronzor is a pain in the rear, packing Levitate to be immune to Earthquake and a neutrality or resistance to everything Tangrowth has besides a Fire-typed Natural Gift, which is a 2HKO. Thankfully Focus Blast is able to do about 45-55% per hit at level 42, although a Pokémon with an actual Fire-type move is recommended. Toxicroak can only 3HKO with Poison Jab; however Tangrowth needs Earthquake, unless you are willing to invest in Natural Gift, in order to deal with it faster, and a critical hit on Poison Jab will turn it into a near OHKO which can be catastrophic if it poisons.
Mars and Jupiter (Spear Pillar, tag battle with rival): Tangrowth has issues dealing with both Golbats at the same time, with the risk of critical hits potentially resulting in it being taken down in one turn if they both go for Air Cutter. The double Bronzor are even more annoying than ever as they will set up dual screens all over Tangrowth's efforts to KO them, especially if Munchlax is still standing on your partner's side. Purugly is the same as last time, expect Aerial Ace probably will do a bit more than Slash and Skuntank has Flamethrower to roast the spaghetti fortress.
Cyrus (Distortion World): Gyarados is free to Shock Wave/Rock Slide into submission, just watch your health since critical Ice Fangs are not pleasant to withstand. Houndoom is the definition of a bad match up, switch out or die to Flamethrower. Crobat is still nasty for the same reasons as last time, only now it has Air Slash instead of Cutter to make you suffer. Honchkrow still has Drill Peak to hurt you with, but Heat Wave is just as nasty - it's always a bad time when the AI has multiple ways to kill you. Lastly, he actually evolved Sneasel. Now it only has a chance at a 2HKO using Ice Punch while Tangrowth smacks it around with any Fighting-type move it gets.
Giratina (Distortion World): Tangrowth does not care about anything Giratina has to hit it with, only being 3HKO'd by Shadow Force. The problem is that this extends both ways, except you are able to heal. Therefore, even if Giratina is even less fazed by your Pokémon's Rock Slides or Grass-type moves than Tangrowth is by Giratina's attacks, you should be able to successfully wall it. Or just throw the Master Ball and be done with it turn one.
Gym #8 - Volkner (Sunyshore City, Electric-type): Jolteon's main option to hit Tangrowth with is Iron Tail, which is both pathetically weak off of its miserable attack stat and inaccuracy. Just hit it until it falls, as this is not a problem. Raichu has Signal Beam, which has a decent chance to 2HKO; however if you are using Tangrowth here, you probably have Earthquake, which has a solid shot at OHKOing back. Maybe drop an X Attack before taking out Jolteon. Luxray wants to, and will take a bite out of Tangrowth through Fire Fang and Ice Fang. However, even with the Rivalry boost, those attacks will only 3HKO, while Earthquake is a 2HKO when unboosted. Tangrowth literally does not care what Electivire has to hit it with, eating up Ice Punch before KOing with Earthquake.
Rival (Pokémon League): Staraptor is still doable as Rock Slide and Shock Wave out damage its Aerial Ace - just be careful of crits. Roserade and Torterra lack ways to do anything resembling decent damage to Tangrowth, feel free to take these as well. Empoleon can take a Focus Blast to the face and lacks much to retaliate with, while Tangrowth can deal with Floatzel's Ice Fangs nicely. You can also overpower Snorlax, with Brick Break being a 3HKO in contrast with Body Slam's 4, although Rest and a 30% paralysis chance can be a pain to deal with. If Staraptor is only 3HKOing with Aerial Ace, the same applies to Heracross, which handily, gets OHKO'd by the same move. Avoid the Fire-types however - both have special STAB moves to burn Tangrowth up with.
Elite Four Aaron (Pokémon League, Bug-type): Yanmega will kill a level 60 Tangrowth if it crits with Bug Buzz. If it does not however, Rock Slide murders it. Scizor is more manageable given its physical slant. X-Scissor is a 3HKO while Earthquake does the same and you need 92 speed in order to get the hits in first. Of course, if you brought Natural Gift, the Fire-type one decimates Scizor. Vespiquen is easy, though, just use Rock Slide and win, since Attack Order is a 4HKO if you've leveled for Cynthia. Drapion falls to Earthquake, end of story. Meanwhile Heracross has Megahorn to 2HKO you with while you can have Aerial Ace to OHKO it back.
Elite Four Bertha (Pokémon League, Ground-type): If it is not named Gliscor, feel free to either Giga Drain or Power Whip it into the ground. Let a Water or Ice-type handle the airborne one, it's for the best given its irritating bulk.
Elite Four Flint (Pokémon League, Fire-type): Nope. Everything here has a STAB Fire move at their disposal to incinerate Tangrowth for even trying to do stuff here.
Elite Four Lucian (Pokémon League, Psychic-type): Tangrowth's questionable special bulk rules out fighting Espeon, Mr. Mime or Alakazam. Bronzong is also far too bulky for non-STAB Focus Blast to deal with either. Just go after Gallade and be careful of critical Psycho Cuts.
Champion Cynthia (Pokémon League): Spiritomb 3HKOs Tangrowth with Dark Pulse. However Power Whip is a 2HKO in exchange while Giga Drain's healing properties should be enough to let Tangrowth come out on top. Avoid Roserade and Togekiss, both are special attackers with STAB moves that take advantage of Tangrowth's weakness and low special defense atop their high stats. Lucario is also an uncomfortable battle as Tangrowth is not outrunning it in the battle of 2HKOs between Aura Sphere and Earthquake/Focus Blast, even with the latter's high chance to OHKO. Milotic is a dangerous opponent to boot, packing Ice Beam to prey on Tangrowth's low special defense and Mirror Coat to slaughter it for using Giga Drain, which does half. Power Whip is an OHKO, though, in comparison to Ice Beam's 2HKO. Garchomp has Flamethrower to avoid dealing with the physical attacker versus physical wall trump card Tangrowth likes to play. So unless you've brought Natural Gift Ice with the sole purpose of demolishing Garchomp (which is still a terrible idea since 252+ Atk Tangrowth Natural Gift vs. 0 HP / 0- Def Garchomp: 176-208 (78.2 - 92.4%) -- guaranteed 2HKO, in addition to its Sitrus berry) stay away. There is not much that can handle Garchomp, and Tangrowth is not among that list.
Post-Game: The sudden drop in coverage moves and lack of double battles in the postgame are good for Tangrowth, although the fight to get into the Battle Frontier is not a fun one due to Flint's presence.
When caught, Tangela will come equipped with Vine Whip, Mega Drain, Bind and either Stun Spore or Poison Powder depending on what level it is caught at. Next up, at level 33, is the move required for evolving your Pokémon, Ancientpower. As a Tangrowth, the first move it tries to learn is Knock Off at level 36, which is nowhere near as close to viable as it is from Generation VI onwards and is not worth using due to its low power. Natural Gift at level 40 is an interesting option, allowing Tangrowth to bring a one-off coverage move if you have enough berries to provide it. At level 43, Slam is outclassed by Return and Strength as a Normal-type option. Tickle is not ideal at level 47, although given the line's impressive defense stat, your Pokémon might be able to salvage some use out of it against certain key physical threats. Wring Out comes at level 50, but given its function is gimmicky at best. Power Whip on the other hand is a valuable addition to a physically focused Tangrowth, coming at level 54, and Block is useless even against the roaming legends because of Tangrowth's garbage speed, being learned at level 57.
While the line's natural movepool leaves a lot to be desired, your Pokémon has access to a wide range of TMs in order to plug the gaps. A noticeable example of this would be Giga Drain, allowing Tangrowth a reliable source of recovery as well as being a decently powered move. Earthquake, Rock Slide, Brick Break and Poison Jab all provide additional coverage on the physical side, allowing Tangrowth to be more aggressive in its role, although those TMs are under competition with other, possibly stronger users. Sludge Bomb fills a similar role in handling opposing Grass-types with Poison Jab on the special spectrum while Focus Blast is a high power option to bust through Steel-types. Shock Wave is really only suitable for taking out Gyarados but Tangrowth is a pretty good choice if you lack a fast Electric-type. The only tutor moves of note that Tangrowth gets are Synthesis and then Sleep Powder from the move relearner. If breeding is an option in your run, Leech Seed is obtainable from a Turtwig or Budew line father.
Physical: Power Whip, Earthquake, Rock Slide, Natural Gift/Poison Jab/Brick Break/Sleep Powder
Special: Giga Drain, Sludge Bomb, Focus Blast, Sleep Powder/Shock Wave/Hidden Power Ice/Hidden Power Fire
Water-type Pokémon: As a pure Grass-type, Tangrowth suffers from a bunch of weaknesses to undermine its good bulk. Thankfully a good Water-type, which should be on your team due to the requirement of using Surf to get to places throughout the game, provides a blanket check against several of the problems types threatening Tangrowth's supremecy. In response, Tangrowth eats opposing Grass and Electric-type Pokémon's attempts to take out its allies.
Rock-type Pokémon: With their exploitable weaknesses to Grass, Water and Ground-type attacks all handily covered by Tangrowth, these Pokémon find themselves able to squash the Flying, Bug and Ice-type Pokémon posing a problem for Tangrowth.
Fast sweepers: Tangrowth's main downfall, outside of its questionable special defense is that it is slow. This can be problematic against certain foes that take the same number of turns as it to KO it when they are faster. However, its physical bulk is great enough to allow it to serve as a valuable switch in for many frail, glass cannon Pokémon bailing out against something they struggle against.
Special tanks/walls: 60 base special defense is not fun to begin with, let alone when you have a weakness to Flamethrower and Ice Beam. However, there are plenty of Pokémon that can handle special attackers without issue. In response, Tangrowth provides a layer of protection against physical attackers.
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.
Tangela Line Ratings
What Nature do I want? Its speed stat is kinda worthless unless you have Chlorophyll, so anything that lowers that is good. Although Tangrowth is pretty good regardless of nature, those that lower defense are the worst options.
Which Ability do I want? Both require Sunny Day to be useful, so they will likely never see use. Chlorophyll has more combat applications with 100/110 offensive stats.
At what point in the game should I be evolved? Before fighting Maylene if you chose to pick it up early, Tangrowth's wider movepool and higher defensive capabilities are crucial in handling Lucario. Otherwise, evolve before fighting the rival in Pastoria.
How good is the Tangela line in a Nuzlocke? It is a Pokémon of extremes. While Tangrowth decimates the mid-game from the moment it evolves due to its movepool and stats, the moment you arrive in Snowpoint things start going south. While it still has its moments, such as being able to flatten four out of the rival's team at the Pokémon League with the right coverage options and can reliably wall Giratina, the rapid increase in special attacks makes its low speed and special bulk a liability in several end game fights. It is still one of the stronger Grass-types in Sinnoh, and will serve you well, although it becomes significantly less splashable the further you take it.
Weaknesses: Flying, Poison, Bug, Fire, Ice
Resistances: Ground, Water, Grass, Electric
Neutralities: Normal, Fighting, Rock, Ghost, Steel, Psychic, Dragon, Dark