Sun is an offensive archetype that primarily abuses the doubled Speed of Chlorophyll users, allowing them to take advantage of their coverage, power, and utility to attempt a sweep. It is similar to teams based around Shellder or Zigzagoon in that it primarily aims to clean with a potent offensive Pokemon, in this case Bellsprout. Like those teams, Sun struggles against a well-prepared team carrying good checks to its sweeper; the most notable Sun checks are defensive Vullaby, defensive Ponyta, Munchlax, and Hippopotas. In addition, Sun-based sweepers are on a timer, and rely heavily on the hazard-weak Vulpix to repeatedly set it up. Despite this, the unpredictability and power of a well-played Bellsprout allows Sun to not only be viable, but extremely threatening.
Offensive Fire-types are an alternative way to abuse Sun over Chlorophyll Pokemon, but this tends to be a less common strategy except when used in conjunction with Bellsprout. It stacks weaknesses with Vulpix, while not having the initial Speed that makes Chlorophyll stacking so strong. Numel used to be the main example of this, but we now have Z-Sunny Day Ponyta and Houndour as well.
Keep in mind that I am discussing dedicated Sun teams; Vulpix sees occasional usage on general offense for its wallbreaking strength, even when not paired with Bellsprout. Those do not fall under the Sun archetype because they aren't based around weather.
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Sun was considered a somewhat viable but ultimately mostly irrelevant strategy in ADV and DPP LC due to the lack of an auto-setter; Rain was the more prevalent manual weather due to a greater variety of strong abusers. The archetype hit an all-time low in gen 5 after Drought Vulpix was banned, as it was easily countered by ubiquitous Sand teams on top of its usual drawbacks. Gen 6 came along and Vulpix was freed; Sun was initially a very dominant strategy due to the presence of Tangela, but after Tangela was banned, it appeared to have lost almost all of its viability.
Shortly after Murkrow and Meditite were banned toward the end of XY,
queenlucy began working on a very irritating team that, until then, would have been laughed off as a gimmick. By the time Misdreavus was banned, XY Sun had been all but perfected. Despite the popularity of Fletchling, Sun was otherwise relatively unprepared for; it soon came to be known as a very effective strategy, even gaining a few ban requests along the way. As the metagame adapted and shifted, Pokemon like Diglett, Vullaby, and Hippopotas became more prominent; Sun began to fade back into obscurity, though it remained a legitimate strategy for the rest of the generation. A few new Sun builds appeared here and there in ORAS, but it would never come close to matching its height in post-Missy until gen 7 rolled along.
With gen 7 came the nerf to Gale Wings, and with the nerf to Gale Wings, the near complete disappearance of Fletchling from the metagame. Just like that, Sun lost its worst enemy; suddenly, Bellsprout was that much harder to prepare for, and Sun could afford to branch out in many different ways. The most notable new Sun build is double Chlorophyll, which accounts for all three uses of Sun in SPL so far; two of those have been wins. This puts double Chlorophyll at nearly the level of the most popular offensive archetypes, including Shellder offense and Fighting spam. The days of Sun being nothing more than a fun gimmick are long gone.
SuMo Sun vs ORAS Sun:
+++ Fletchling was able to instantly shut down a Bellsprout sweep in gen 6 with its priority Acrobatics; it is no longer competitively relevant in gen 7.
++ Porygon was by far the most common defensive Pokemon in gen 6, and checked Sun quite well with its standard Download and defensive Trace sets.
++ The addition of Z-moves allow Sun sweepers to bypass bulky Pokemon that they would otherwise be walled against. This especially benefits teams with multiple Chlorophyll sweepers.
++ Staryu is now incredibly easy to include on a team, and benefits Sun both as a strong spinner and as a switchin opportunity for Bellsprout.
+ Sucker Punch has been nerfed and Pawniard usage has decreased, which helps because strong priority is quite troublesome against a weakened Sun sweeper.
+ Fairy-types are strong right now, granting Bellsprout and Vulpix more switchin opportunities.
+ Carvanha usage has decreased slightly, which results from how good Timburr is.
~ Timburr is often specially frailer, allowing Sun sweepers to break through it earlier on. However, it now more frequently carries Ice Punch.
~ Vulpix has a good matchup against Alolan Vulpix and Hail teams, but Bellsprout dislikes having Sun removed.
~ Vullaby has become more common, but is often a frail sweeping or Scarf variant, which Bellsprout does not have as much difficulty breaking through.
- Scarf users more frequently reach 27 Speed or higher, allowing them to outspeed 13 Speed Bellsprout. This is a direct adaptation to Sun's prevalence.
- Alolan Grimer is one of the most splashable Pokemon in the metagame and acts as a decent Sun check.
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Most Sun teams can be classified into one of the following subarchetypes.
Traditional Sun: an offensive build that aims to get Bellsprout, the team's main wall-breaker and sweeper, into play as often as possible. When Sun was first brought into the limelight in late XY, it was with this sort of build.
Key Pokemon: Vulpix, Bellsprout, Mienfoo, Archen, Staryu, Diglett, Onix, Numel, Pawniard, Snubbull
Shine Bright Like a Vulpix
Sun Balance: a more defensive build is utilized alongside the basic core of Vulpix and Bellsprout in a mostly detached manner, aiming to whittle the opposition down until Bellsprout can clean without trouble late in the match. The safest way to use Sun in terms of match-up, but it takes advantage of Bellsprout the least.
Key Pokemon: Vulpix, Bellsprout, Mienfoo, Archen, Staryu, Slowpoke, Mareanie, various defensive cores
Double Chlorophyll: this hyper offensive build takes advantage of both Bellsprout and Bulbasaur to put absurd amounts of pressure on shared checks, and also makes both Chlorophyll users more expendable, at the cost of stacking weaknesses and a reliance on Sun being up.
Key Pokemon: Vulpix, Bellsprout, Bulbasaur, Mienfoo, Archen, Staryu, Diglett, Kabuto, Onix
Double Fire: by running Ponyta or Houndour alongside Vulpix and Bellsprout, you gain an extra Sunny Day user to support Bellsprout as well as a strong secondary sweeper. Similarly to double Chlorophyll, however, you stack weaknesses, and without the Speed boost from Chlorophyll, other hyper offensive archetypes become troublesome.
Key Pokemon: Vulpix, Bellsprout, Ponyta, Numel, Houndour, Mienfoo, Archen, Staryu, Slowpoke, Mareanie
Sample teams (Z-Ponyta Sun is the first SuMo team listed)
Triple Chlorophyll: an even more extreme take on double Chlorophyll, but at this point, stacking so many weaknesses leads to a very large degree of unreliability; expect to see outright unwinnable match-ups more often.
Key Pokemon: Vulpix, Bellsprout, Bulbasaur, Cherubi, Exeggcute, Riolu, Cottonee, Archen, Kabuto, Onix
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Here are some things that every, or almost every competitive Sun team should have:
Vulpix, the most reliable Sun setter and abuser.
Backup Sun setters: Diglett Cottonee, Riolu
Bellsprout, the most threatening Sun abuser and its main sweeper. A possible exception could be made for teams based purely on Fire spam, but these would generally be improved by Bellsprout anyway, as Bellsprout synergizes with Fire-types defensively and is generally just too good with Sun support to pass up.
Backup Chlorophyll sweepers: Bulbasaur, Cherubi, Exeggcute
A
Stealth Rock user. All offensive teams should have hazards to secure key KOs and take advantage of forced switches, but Sun in particular benefits from Stealth Rock as many of its checks, such as Flying- and Fire-types, are weak to it, and Sun teams have the means to heavily pressure Staryu.
Stealth Rock setters for Sun: Archen, Diglett, Kabuto, Onix, Pawniard, Cranidos, Omanyte
A
Rapid Spin or Defog user. Since a Sun abuser outside of Vulpix will have a maximum of 7 turns to sweep, it's important to keep Vulpix healthy so that it can set Sun up repeatedly. Extremely offensive Sun teams with multiple reliable Sun setters can potentially forgo this, but doing so still isn't ideal.
Hazard removal for Sun: Archen, Staryu, Kabuto
A solid
Ponyta check. Hippopotas and Munchlax are uncommon enough to acceptably risk a weak match-up against, and birds naturally have a good amount of counterplay, but if you're not prepared for Flame Charge or Z-Sunny Day Ponyta, it will ruin your (sunny) day. Ponyta comes in on Vulpix for free and can soft check Bellsprout even if it doesn't sweep.
Ponyta checks for Sun: Archen, Staryu, Diglett, Kabuto, Onix, Slowpoke, Ponyta, Numel, Mareanie, Houndour, Cranidos, Chinchou, Omanyte
A
bird check. This doesn't have to be especially reliable, because most birds lack switch-in opportunities and can simply be worn down, as well as revenge-killed by Bellsprout under the Sun when weakened. However, being completely unprepared for them is begging to be swept by bird spam or a well played offensive Vullaby.
Bird checks for Sun: Archen, Staryu, Kabuto, Onix, Slowpoke, Magnemite, Cranidos, Chinchou, Omanyte
And some things that most Sun teams should have:
VoltTurn. This is enormously helpful to get Vulpix and Chlorophyll abusers into play safely, as they often struggle to switch in otherwise with their low bulk.
VoltTurn users for Sun: Mienfoo, Archen, Magnemite, Chinchou
Knock Off. Bellsprout fails to OHKO many bulky Eviolite users, even if it is carrying a Life Orb; removing their Eviolites gives Bellsprout a much easier time sweeping.
Knock Off users for Sun: Bellsprout, Mienfoo, Archen, Bulbasaur, Kabuto, Pawniard, Cottonee, Timburr, Omanyte
A
Pawniard check. Pawniard's Sucker Punch is the strongest priority against Chlorophyll users that you will commonly see; Bellsprout and Bulbasaur resist the other two important priority move types in Fighting and Water.
Pawniard checks for Sun: Mienfoo, Diglett, Ponyta, Numel, Houndour, Riolu, Timburr
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Now I'll try and describe some good Pokemon to include on Sun teams.
5/5 - All competitive Sun teams should have them.
Vulpix: The only auto-setter of Sun in LC and the reason why Sun is viable at all. Having an auto-setter allows sun to be set up in a huge amount of situations where it would otherwise be costly or impossible to set. Vulpix also synergizes defensively with Chlorophyll abusers and offensively with other Fire-types, in addition to being a decent Pokemon on its own, leaving no reason not to use it on any competitive Sun team.
Bellsprout: The gold standard for Sun abusers and the reason why Sun is such a strong archetype. Access to both pseudo-STAB Weather Ball and STAB Sludge Bomb makes it more difficult to switch into than any other Chlorophyll abuser, on top of some more niche options such as Sucker Punch and Knock Off to make it the most versatile of them as well. Its strength and unpredictability rank it as one the most threatening offensive Pokemon under the Sun, and the only reason to use other Sun abusers is to take advantage of their offensive synergy with Bellsprout. Eviolite, Life Orb, Poisonium-Z, and Grassium-Z with Sleep Powder or Growth in the last slot are the most common ways to use Bellsprout.
4/5 - These offer a huge amount to sun teams; expect to see about as many sun teams with them as without.
Mienfoo: On top of being one of LC's best Pokemon to begin with, Eviolite Mienfoo's utility is especially appreciated for Sun teams, making it about as close to a mandatory support Pokemon for Sun as you can get, excluding Vulpix. Knock Off wears down bulky Pokemon that Chlorophyll sweepers struggle to OHKO; Regenerator allows it to check Pawniard throughout the match; and, most importantly, Regenerator + U-turn lets Mienfoo get Vulpix in safely throughout the match. Slow Mienfoo is the most common variant found on Sun to get Vulpix in safely with U-turn against more threats, but faster spreads to better check Pawniard and get off a fast Taunt are viable as well.
Archen: Though strong offensively, Sun cores need a lot of support to pull off a sweep against a solid team. Archen offers so much in a single slot that it can be hard to pass up; even though it can't do everything at once, it can always offer something helpful while the rest of the team patches up any remaining holes. Defog, Stealth Rock, checking birds, soft checking Ponyta, Knock Off, and U-turn are all things Archen can attempt to do while maintaining a strong offensive presence. Berry Juice Archen is more common for its offensive presence, but Eviolite Archen is fine as well.
Staryu: It may seem odd to run a Water-type on Sun, but the three most threatening Pokemon to Sun are Ponyta, Hippopotas, and Munchlax; Staryu happens to hard check the first two, while Munchlax is relatively uncommon. Furthermore, Staryu provides invaluable Rapid Spin support so that Vulpix can get into play more often, and forms a Fire-Water-Grass core with Vulpix and Bellsprout, making it an extremely strong option for a variety of Sun teams despite having its Scald weakened. Eviolite variants are preferred to better check what they need to while not being as badly held back by a weakened STAB move.
3/5 - Great picks for a variety of sun builds, but a bit less splashable than the above.
Diglett: Being able to trap and weaken Ponyta with the Focus Sash variant is nice, as is a well-timed Tectonic Rage on a bulky Pokemon. The main use for Diglett, however, is trapping Pawniard, Abra, and SturdyJuice Magnemite so that Chlorophyll sweepers can save Sleep Powder for something else. Diglett also has a variety of other tools up its sleeve to make it a very useful support Pokemon for Sun, including Stealth Rock, Sucker Punch, Memento, an immunity to Volt Switch, and Sunny Day.
Bulbasaur: Though outclassed by Bellsprout on traditional Sun teams since Weather Ball isn't compatible with Chlorophyll, Bulbasaur is definitely the best choice for double Chlorophyll, as its checks are identical to Bellsprout's, allowing one to support the other's Growth sweep with a well-timed Sleep Powder or Z-move. Bulbasaur's advantage over Bellsprout is its higher Speed to deal with certain troublesome Choice Scarf users or setup sweepers. It also has slightly better bulk, beats Chespin, and is quite threatening in its own right.
Kabuto: A reasonable alternative to Archen for its ability to more reliably check defensive Ponyta and birds, on top of the advantages of Rapid Spin over Defog. Its relative lack of offensive presence due to weak STAB moves and lower Attack generally makes it the lesser choice, but it is seen more often on double and triple Chlorophyll teams that are especially vulnerable to defensive Ponyta and cannot find room to fit a backup check.
Onix: Generally paired with Staryu to serve as the bird check of the team, as Staryu can Rapid Spin for Onix to take advantage of SturdyJuice. In addition to checking birds, Onix can check Ponyta, deter Volt Switch to give Vulpix and Bellsprout more opportunities to come in, serve as a decent safety net if it can come in at full health, and is arguably the most reliable Stealth Rock setter in the metagame, making it a great choice for role compression.
2/5 - Decent but niche picks for specific roles.
Slowpoke: One of the most reliable Ponyta, smasher, and Ground checks in the metagame. Staryu tends to be used more for the sake of role compression with its access to Rapid Spin, as well as Slowpoke's weakness to Vullaby, but Slowpoke can be paired with Archen in particular to good effect.
Ponyta: Fire spam is a viable strategy to muscle through balance especially, as well as providing an easy way to fit in a secondary Sun setter. Offensive Ponyta is an ideal candidate for a partner to Vulpix thanks to its Speed and power.
Numel: Simple Numel is interesting in that although it is relatively tame after a single turn of setup, it is among the most threatening Pokemon in the metagame after two. Sun makes Numel's Simple Growth even more terrifying, and it lets Numel withstand weak Scalds while setting up.
Mareanie: Mareanie is the most reliable Ponyta check in the game, granting it a similar role to Slowpoke as a good back-up Fire check on teams utilizing Archen. It has very little offensive presence and is prone to being trapped by Diglett, but handles Fighting-types quite well.
Pawniard: Scarf Pawniard is a decent choice for role compression on Sun, providing Knock Off, Pursuit, and potentially Stealth Rock support. However, it stacks weaknesses to Ponyta and doesn't offer much defensively, which is why it is less prominent than it was for gen 6 Sun.
Snubbull: Despite stacking weaknesses to Fire-types, Snubbull is useful on offense in general for being an extremely solid Fighting check while not losing momentum as badly as Spritzee. It doesn't offer much else, but that alone can grant it a team slot and made it a staple of gen 6 sun.
Houndour: The main competition for Ponyta as a z-Sunny Day user, offering strong priority in Sucker Punch and stronger Fire Blasts/Solar Beams in exchange for Ponyta's higher initial Speed and access to Hypnosis.
1/5 - Usable on very specific sun builds.
Cherubi: If you're really into fast offensive Grass-types and want to go for triple Sun, Cherubi tends to be the best choice, as its access to Weather Ball makes it reasonably threatening in its own right, and it can support Vulpix or its fellow Chlorophyll abusers with Healing Wish. However, it's outclassed on double Chlorophyll by Bulbasaur due to its lack of a useful Poison typing and Sleep Powder, as well as overall worse stats.
Magnemite: Though it was a better choice for Sun when Misdreavus and Fletchling were relevant, Magnemite still serves as a decent bird check, slow Volt Switcher, and either a Pawniard trapper or safety net, depending on whether it chooses to run Magnet Pull or SturdyJuice. It stacks some weaknesses, however.
Cottonee: Double and triple Chlorophyll may appreciate a reliable secondary Sun setter. Cottonee acts as this through Prankster Sunny Day, and can also attempt to wear down checks to Chlorophyll abusers with Knock Off. It can be run with Heat Rock or Eject Button.
Riolu: The more defensive synergy minded Prankster Sun setter compared to Cottonee, Riolu has the benefit of soft checking Pawniard and not stacking weaknesses.
Cranidos: Usable for role compression to set up rocks, check Flying-types, and uniquely over other Rock-types bar Larvitar, Pursuit trap weakened Flying-types and possibly Abra. However, Archen's and Onix's advantages tend to be more useful overall.
Exeggcute: It has some real advantages over Bulbasaur on double Chlorophyll and Cherubi on triple Chlorophyll due to its access to STAB Psychic, great physical bulk, and ability to beat most Abra. The reason it is generally inferior on double Chlorophyll is that it is quite weak initially, needing Life Orb or some prior damage to OHKO even fast Eviolite Mienfoo, and being weak to U-turn and Knock Off actually makes it less reliable of a Fighting switch-in.
Chinchou: It's a good check to Ponyta and birds, and also offers a slow Volt Switch to get Vulpix in, but is prone to being worn down, and can't stall out Sun with a recovery move the way Staryu, Slowpoke, and Mareanie can.
Timburr: If you are badly in need of a soft check to smashers, or would like some strong priority for Pawniard and Carvanha, Timburr is an understandable alternative to Mienfoo, but U-turn is hard to give up.
Omanyte: Kabuto tends to be compared to hazard Omanyte, so Omanyte is a somewhat reasonable alternative due to its access to Spikes. However, hazard removal is extremely important to keep Vulpix healthy, and Omanyte does not synergize well with Staryu or Archen; furthermore, its other advantage of superior offensive presence is mitigated by Sun.
0/5 - These potentially have uses on sun but are difficult to justify competitively; they tend to be badly outclassed by other choices. This is where boring old levi criticizes your attempt at creativity.
Deerling: I suppose this is the most justifiable of the unviable Sun Pokemon. Jump Kick lets Deerling break through Munchlax, but Munchlax is too uncommon to warrant dedicating an entire Pokemon to beating. The higher Speed lets it outrun +2 15 Speed Vullaby, as well as Scarf Diglett and Elekid, but these are relatively specific scenarios. On the other hand, Deerling's drawbacks over other Chlorophyll Pokemon are huge. As it is forced to go physical due to its abysmal Special Attack, Deerling sorely misses out on Fire coverage and the power of Solar Beam. This is coupled with Deerling's lack of Sleep Powder, inability to boost its Attack outside of Work Up, and naturally mediocre Attack, rendering it far less threatening than other Chlorophyll sweepers.
Oddish: Oddish may be tempting to use on double or triple Chlorophyll for its decent bulk, but it stacks weaknesses unnecessarily on triple Chlorophyll. On double Chlorophyll, its awful Speed tier forces it to run Timid, generally leaving it outclassed by the more versatile Bulbasaur.
Torchic: Speed Boost + Sun-boosted Fire Blast looks like a very nice combination. Unfortunately, Torchic has nothing else offensively; its lack of Solar Beam means that Ponyta and Houndour are able to threaten a far greater variety of teams. Also, keep in mind that we're still stacking weaknesses with Vulpix here
Petilil: Another Healing Wish Chlorophyll Pokemon, trading Weather Ball for Sleep Powder over Cherubi. However, due to Sleep Clause, only one of the triple Chlorophyll core should really be running Sleep Powder, making access to a strong coverage move in Weather Ball the far superior benefit..
Litleo: You may compare Litleo's stats to Houndour's and Ponyta's and think that it has a niche, but missing out on Flash Fire is a huge loss for an archetype that tends to be weak to opposing Fire-types. Furthermore, it lacks Houndour's priority and Ponyta's great Speed tier, leaving it vulnerable to offensive builds and generally outclassed.
Dwebble: Often compared to hazard Omanyte in its niche. It synergizes with Staryu a little bit better - too bad it offers absolutely nothing for Sun outside of hazards and a soft bird check. It's not worth using on Sun over better role compression Pokemon.
Larvitar: It gets Pursuit, soft checks birds, and shuts down defensive Ponyta. It's also extremely weak initially, loses to Volt Switch users despite its immunity, and is generally not very threatening; it's simply too underwhelming of a Pokemon to warrant competitive use.
Purrloin: Between its low offensive stats, terrible bulk, and lack of resistances, Purrloin is the perfect combination of mediocrity to not ever be worth using over its Prankster brethen.
Salandit: Poison STAB may seem like a noteworthy niche over Ponyta and Houndour, but it comes at the cost of the far more useful Solar Beam. Salandit also misses out on Flash Fire, Ponyta's Speed, and Houndour's strong priority.
Darumaka: Impressive as a Sun-boosted Hustle Flare Blitz may be, Darumaka kills itself off too quickly, too unreliable, too slow without Choice Scarf (stopping it from setting up Sunny Day on its own), and too easily revenge-killed to warrant the hassle of getting it into play while Sun is up.
Sewaddle: Chlorophyll is generally enough for Speed control; Sticky Web is a bit overkill. If you're that worried about Scarf users, it's much better just to account for them defensively or run a positive Speed nature instead of using a generally mediocre Pokemon like Sewaddle.
Hoppip: Despite an interesting set of STAB moves and access to U-turn, Memento, and Sleep Powder, Hoppip's absurdly low stats leave it trivial to deal with for any solid team. Hoppip's biggest strength is how menacing it is - use that to your advantage.
Charmander: Sigh, looks like someone really wants to use Charmander. Charmander is really just not viable competitively. It's revenge-killed much more easily than Ponyta or Houndour, is too frail from Solar Power to really attempt to set up Sun on its own, has no immunities or bulk to get itself into play on, and is completely reliant on Vulpix to be of any use.
Seedot: I guess it gets Defog?
Sunkern: ha ha
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Checking Sun may seem daunting due to Bellsprout's fantastic coverage, but there are a few Pokemon that Sun teams often struggle against.
Defensive Ponyta. Eviolite Ponyta hard counters Vulpix, easily stalling out Fire Blast's PP and OHKOing after Stealth Rock in return with a Sun-boosted Flare Blitz. Flame Charge Ponyta can outspeed 13 Speed Bellsprout after a single boost, allowing it to effortlessly clean unprepared Sun teams. Ponyta can also switch into Bellsprout somewhat after Sleep Clause has been activated, although it is 2HKOed by Eviolite Bellsprout's Sludge Bomb after Stealth Rock, and takes a lot from Acid Downpour. Offensive Ponyta is less reliable at checking Vulpix and Bellsprout but is still fairly threatening.
Carvanha. If Carvanha nets enough Speed booosts, it outspeeds Chlorophyll users and heavily damages them with Crunch; a Special Carvanha variant can cleanly OHKO Eviolite Bellsprout with Ice Beam. It also stalls out precious Sun turns with Protect. However, Carvanha's Water-type STAB moves have their damage reduced by Sun.
Bulky Vullaby. On top of generally being a fantastic pivot and Knock Off spreader, bulky Vullaby makes for a strong answer to Sun. Its naturally high Special bulk allows it to withstand Bellsprout's attacks, and Overcoat lets it switch in on Sleep Powder. However, the standard 25 HP/14 SpD variant is 2HKOed by Life Orb Bellsprout's Weather Ball; running more Special Defense to reach 16 SpD helps to prevent this, but it is still 2HKOed after Stealth Rock. In addition, Vullaby should be wary of Acid Downpour, as this can KO after some prior damage and otherwise leaves Vullaby too weak to do much else in the game.
Mareanie. The most solid Fire check in the tier, Mareanie ensures that Vulpix, Ponyta, and Houndour will not be offensive threats until Mareanie is trapped by Diglett. It also has the raw bulk to stall out Sun turns with Recover against Chlorophyll sweepers if they lack Growth and Sleep Clause has been activated.
Alolan Grimer. Grimer resists Bellsprout's STAB moves and can avoid the OHKO from Bellsprout's Weather Ball without issue, although it can be 2HKOed by the right combination of moves by all Bellsprout variants after Stealth Rock. Even if it is hit by Sleep Powder, it has the bulk to stall out some Sun turns.
Life Orb Torchic. Definitely the most offensively threatening Pokemon for Sun. Vulpix is OHKOed by Sun-boosted Fire Blast after Stealth Rock and even 23 HP/14 SpD Mienfoo has a good chance of being OHKOed; Staryu is 2HKOed by HP Grass, and defensive variants are unable to OHKO Torchic because of their weakened STAB attacks. Onix and Kabuto are OHKOed by HP Grass. LO Torchic becomes much easier to deal with if niche options like Mareanie and Numel are used, however.
Hippopotas. Specially Defensive Hippopotas is the go-to check for teams that desperately need a Sun check. By converting Weather Ball into a Rock-type move and causing Solar Beam to take up an extra turn to charge, Hippopotas effortlessly walls standard Bellsprout variants and leaves it prone to revenge-killers. It also walls Vulpix, though it dislikes burns. The main thing to watch out for is Giga Drain on secondary Chlorophyll sweepers like Bulbasaur especially, as well as the rare Bloom Doom Chlorophyll sweeper.
Amaura. Similarly to Hippopotas, Amaura shuts down Bellsprout by setting up a different weather, causing Weather Ball to become Ice-type and Solar Beam to require a charge-up turn. Also similarly to Hippopotas, it fears Giga Drain Chlorophyll sweepers and the occasional Bloom Doom. Amaura's lack of recovery means that it struggles to switch into Vulpix repeatedly.
Munchlax. This catch-all Special wall is one of the sturdiest Sun checks around, with the Eviolite variant withstanding even a Growth-boosted Acid Downpour from Bellsprout, allowing it to retaliate with a Sun-boosted Fire Punch. In addition, Munchlax shuts down most Fire-types, including Vulpix and any attempts at Fire spam. However, Munchlax's drawbacks in the current metagame may render it difficult to fit onto a team.
Houndour. Houndour completely walls Vulpix thanks to Flash Fire, is generally difficult to switch into, and can threaten a weakened Bellsprout with a powerful Sucker Punch if Sleep Clause is activated. Eviolite Houndour is often considered a mediocre set but is able to withstand Life Orb Bellsprout's Sludge Bomb after Stealth Rock to retaliate with a Sun-boosted Fire Blast or Flame Charge.
Scarf Elekid. If you're going for the unexpected Sun counterteam, this can be a fun choice. Sun sweepers rarely reach more than 28 Speed, allowing Elekid to outspeed them and do a good amount of damage with Psychic. However, Elekid is extremely weak for an offensive Pokemon without Life Orb, so this should only be considered if you have good reason to expect Sun.
Alolan Vulpix and Snover. Although they lose badly to Vulpix and do not enjoy switching in on Bellsprout's Sludge Bomb, they can come in on a predicted Solar Beam or Weather Ball and cut Bellsprout's sweep short.
Scarf Doduo and Gastly. These are the more common 27 Speed Scarf users. They are fast enough to revenge-kill 13 Speed Bellsprout, but are outsped by 14 Speed Bellsprout and Bulbasaur. Gastly also needs some prior damage to KO Eviolite Bellsprout.
Scarf Diglett and Taillow. Some more niche Scarf users that are more reliably able to outspeed Chlorophyll sweepers and revenge-kill them once weakened.
Focus Sash Abra, Gastly, and Diglett. Abra, Gastly, and Diglett are common Focus Sash users that are able to revenge-kill Bellsprout if they can keep their Focus Sashes intact, though Diglett and Gastly need some prior damage. At worst, they are hit by Sleep Powder and stall out some Sun turns or go for the one turn sleep. Diglett can also revenge-kill Vulpix, or even directly switch into Vulpix's Fire Blast or Energy Ball (assuming Vulpix isn't Quick Attack), as well as Will-O-Wisp if Vulpix has taken Stealth Rock damage, and KO with Earthquake; this is a risky move due to Flame Charge Vulpix, however.
Aipom, Meowth, and Fake Out Mienfoo. Fake Out users are able to simultaneously get some chip damage in on Sun sweepers and stall out Sun turns, as well as revenge-kill a weakened Chlorophyll sweeper. They also all easily have the power to force Vulpix out.
Wynaut. If Sleep Clause is activated and the Chlorophyll user does not carry Growth, Wynaut can actually risk directly switching into the Chlorophyll sweeper and clicking Mirror Coat. It also badly threatens Chlorophyll sweepers on the revenge-kill by potentially locking them into Growth with Encore, which is relatively safe to use thanks to Wynaut's naturally good Special bulk coupled with Berry Juice allowing it to avoid the 2HKO from most attacks. Vulpix has counterplay with Will-O-Wisp but Wynaut can still stall out Sun turns.
SturdyJuice users. If Sturdy is kept intact, SturdyJuice users can withstand an attack from a Chlorophyll sweeper or Vulpix and hit back hard, or at least stall out Sun turns if slept. Endure SturdyJuice Magnemite can attempt to stall Sun out fully with Recycle, after which it walls Bellsprout.
Sticky Web. Due to stats rounding down, 13 Speed Bellsprout reaches 17 Speed after Chlorophyll and Sticky Web, while 14 Speed Bellsprout and Bulbasaur reach 18 Speed. This allows for faster Webs abusers like Abra, Gastly, and Doduo to revenge-kill them. Vulpix is a non-issue for most Webs teams.
Strong Priority. Once Chlorophyll sweepers have taken enough chip damage, they can be taken out by various priority moves.
There are a few other niche options to deal with Sun, such as Chlorophyll Deerling, Chespin, Fletchling, and Copycat Riolu, but these are generally considered unviable.
If you've run out of Sun checks and there is a Chlorophyll sweeper on the field, smart switches into resistances can help to stall out Sun turns. This can also be used to get Sleep Clause activated on a Pokemon that Bellsprout doesn't need to put to sleep, so that you can use your Sun check without worrying about Sleep Powder. Be careful of Growth, however.
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I was planning on doing posts like this one for a few other effective offensive archetypes (fish spam, Zigzagoon offense, webs), but this post turned out to be longer than I thought, so I probably won't get around to it.
So what do you guys think of Sun? Do you think it's too strong, or still not that good? Are there any Sun teams that you have used that this post might not have covered adequately, or checks that I missed?