I think Jynx should rise from D to B-. Although this may seem drastic, Jynx has a massive niche in this metagame. There are two sets I think are worth mentioning; primarily, Jynx's best set in my opinion, a lead focus sash set.
Jynx (F) @ Focus Sash
Ability: Dry Skin
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Lovely Kiss
- Ice Beam
- Shadow Ball
- Nasty Plot
Unfortunately for almost every sleep-sweeper, generation 6 brought a nerf where sleep powder and spore can't induce sleep on grass-types and pokemon with overcoat. Fortunately, Jynx has Lovely Kiss, which is 75% accurate like sleep powder, but hits grass-types and Escavalier. This, combined with its focus sash and great base 95 speed, lets Jynx put 1 pokemon to sleep almost every game. After that, if your sash is still maintained, you can proceed to set up a nasty plot. Jynx's +2 ice beam OHKOs Moltres, Hitmonlee, Spdef Rhyperior, Sharpedo, Banette, Spdef Amoonguss, Offensive Drapion, Speedy Exploud, and Weezing. Since ice is such a great offensive typing, and Jynx has a nasty base 115 special attack, it finds many opportunities to dig massive holes into teams, or even sweep some bulkier teams. Shadow Ball seems curious on this set as opposed to psychic or Focus Blast, but if you look at some of the top used pokemon in the tier, Shadow Ball provides necessary coverage to leave Jynx unwalled by some of the top threats. Delphox, Slowking, Doublade, Bronzong, and Steel-types in general all resist psychic and ice type moves. Shadow Ball is super-effective on these pokemon, and can OHKO Doublade, Delphox, and physically defensive Bronzong at +2. Shadow Ball also provides Neutrality to Durant, who gets OHKOd at +2, and Escavalier, who is easier to passively damage.
Outside of this set, there isn't much else to run in RU. The prominence of Slowking and Delphox make sub nasty plot near-impossible to pull off. Life orb 3 attacks is the only other potential set to run in RU, providing extra power and coverage in the form of Psychic, but doesn't get the guaranteed sleep that this set gets, and its frailty makes it hard to switch in and out of the field often.
Overall, with Zoroark and Yanmega gone, Jynx can find a new niche as a free sleep-inducer against almost every team. Base 95 is even faster than threats like Meloetta and Moltres, and Jynx possesses massive power to match it. That, in conjunction with its fantastic offensive ice-typing and ability that makes it immune to water type attacks, make Jynx a big threat in RU.