Ah Jynx, easily one of, if not the most influential pokemon of all of NU. Not preparing for this can lead to a harsh loss, but is she manageable otherwise?
Pros: Base 115 Special Attack means she has very little trouble OHKOing anything she hits SE, 95 Speed is a huge step up from the 80-85 range inhabited by former meta-shaping threats in Gardevoir, Sawk and Braviary. Previously, anything that could hit that range can considered usable (Arbok) and anything above that range are much more notable threats (Zangoose, Kangaskhan, Sawsbuck, Rotoms) than they are today, but now base 95 is the speed to hit. I wouldn't say Jynx is solely responsible for the speed creep, but she is definitely a big contributer. If you can outspeed Jynx, you stand a decent shot at success already, since Jynx's success relies hugely on being able to outspeed opponents, which she can do against a good majority of the tier.
Dry Skin grants Jynx one of the greatest gifts she could ask for: free switches. Every Water-type has to be wary about spamming their strongest / only attack whenever Jynx is lurking around, and must aim to strike her down with other moves (usually physical), such as Megahorn from Samurott (even special variants), Stone Edge from Carracosta and Earthquake from Seismitoad. As a result, other Water-types that cannot heavily damage Jynx, such as Ludicolo, Wartortle or Alomomola, are pegged down a notch in terms of usability. The fact that I even saw a Gyro Ball Wartortle have shown just how important it is to not give Jynx free turns to setup.
Jynx's Ice and Psychic typing gives her fantastic coverage, although Ice is so good on its own due to no immunities and great SE coverage that most Jynx flat out forgo Psychic. Due to her speed and access to Ice Beam, Jynx is the fastest and likely the most reliable Ice attacker we have in NU to date: Glaceon is powerful but too slow, Articuno has dual STABs but isn't too powerful and is massively SR weak, Regice's coverage is great but is much too slow, and Rotom-F does not have the reliable Ice Beam.
Jynx's movepool, oh boy. This may be the biggest factor for Jynx's suspecting, because with moves like Lovely Kiss, Nasty Plot, Focus Blast, Trick and Substitute, as well as STAB Ice Beam, Psychic and Psyshock at her disposal, Jynx can threaten any team archetype if she gets just one chance to rev up.
- Lovely Kiss is the most notable move here, as Jynx can use her speed to shut down an opponent and get away with it easily, but that isn't the worst part. Jynx has the power (or at least, not yet) to easily destroy your sleeping pokemon should it attempt to stay in and wake up, so cornered people are either forced to sac one of their pokemon to Lovely Kiss and send in their counter/check later, or equip the counter/check with Sleep Talk. Using up a whole moveslot primarily to deal with one pokemon signifies how much of an impact Jynx has had on the tier. It's fine and dandy if your counter happens to utilise RestTalk, but any pokemon relying on that isn't seen very often in high level play.
- Substitute is the next big thing about Jynx. While Substitute helps a lot of pokemon, it is especially deadly in Jynx's hands when you consider her speed, ability, typing, decent special bulk, sleep-inducing move and setup move. Sub allows Jynx to block status such as Toxic Alomomola, Sleep Powder Tangela and Thunder Wave Musharna, who usually do not sport the means to threaten Jynx directly. Sub also provides a safety buffer against fast-waking opponents or faster attacks. What this means is that even if you have 5 pokemon that are faster than Jynx and can immediately KO her, if Jynx gets in on that one pokemon that cannot do much to Jynx, you'll lose all momentum and possibly a couple of pokemon (one, to sleep, the other from a KO).
- Other moves can make things even easier for Jynx: Focus Blast maims bulky Steels (Probopass, Bastiodon) and Normals (Thick Fat Miltank, Licklicky) and Regice; Psyshock owns specially bulky mons (Mantine, Munchlax, Flareon, Articuno, Regice), Nasty Plot overpower stall or KOs anything in offense; Trick screws up stall/defense and grants Jynx the freedom to switch attacks;.
As far as items go, Jynx commonly makes use of Leftovers and Choice Scarf, because they are excellent in helping Jynx to sweep. Leftovers combos with Substitute and gives Jynx ample time to build herself up for the big sweep. Choice Scarf means Jynx comes out guns blazing, using fast and powerful Ice Attacks to steamroll over much of the tier, or use a quick Lovely Kiss to stop a threat she cannot KO. If she is up against a more defensive team, she can Trick her Scarf away to not only cripple a pokemon, but also have the freedom to switch moves, more than likely Lovely Kissing something to put 2 pokemon out of commission.
Cons: Absolutely horrid base HP and Defense means she would take crazy damage from any kind of physical hit. Any faster mon/Scarfer with a physical move is likely to KO Jynx right there. Most priority moves (bar Aqua Jet and Ice Shard) can also hurt Jynx significantly. Pursuit can likely KO even a remotely weakened Jynx regardless of whether she stays in or not. Her frailty will also punish her should she miss a Lovely Kiss or Focus Blast.
Her typing may be strong offensively, but easily exploited defensively, some of which are weaknesses Gardevoir lacks. Firstly, the hazard weakness. Stealth Rock, Spikes and Toxic Spikes all tear Jynx a new one, especially if more than one is on the field at a time. This restricts Jynx so that she cannot switch in and out as freely, or have her sweeping time shortened. Jynx also bears weaknesses to Fire and Steel, meaning faster Fire-types such as Charizard, Rapidash, Simisear, Jolly +1 (+2 for Scarf Jynx) Combusken, as well as Bullet Punch can stop Jynx, although slower and bulkier Fires (Flareon, Camerupt) or Steels (Metang, Wormadam-T) can simply weather the attack and OHKO back.
Conclusion: Jynx's advantages far outweigh her disadvantages, especially when some of the latter can still be worked around (Sucker Punch is risky against Jynx, and the hazard weakness is mitigated considering Jynx doesn't need to switch all that much).
I am still torn on Jynx's suspect placing, if anyone has anything to add to my list of pros and cons feel free to let me know~