Jynx is the ugliest Pokemon ever. Seriously. When a new game comes out, I pray that this abomination of nature does not get an evolution. If it does, all computers will cease to function and cause blackouts.
Aesthetics aside, Jynx's capabilities in combat are above average. She's not a stellar Pokemon by any stretch of the imagination. It's easy to see why. The first problem is her stats. Base 115 special attack is nice, but base 95 speed just doesn't cut it anymore. Paired with poor HP and defense stats, Jynx won't be able to do much. This leads to problem 2: type and weaknesses. As an ice type, Jynx will take 25% damage from Stealth Rock. In addition, she has weaknesses to fire, steel, and rock. As a psychic type, Jynx is weak to Pursuit. Throw in heavy exposure to Spikes, Toxic Spikes, and priority moves and Jynx's short lifespan gets even shorter. The last (and biggest) problem is competition. Toxicroak is a far superior Dry Skin abuser to counter rain teams. As a beatstick on hail teams, Kyurem reigns supreme.
Is there anything that makes Jynx worth using? Yes. Jynx has access to a large-ish movepool with Nasty Plot and her signature move Lovely Kiss. These moves allow Jynx to hit harder than Kyurem while allowing safe stat boosting. Jynx can also PerishTrap, and has access to Wish, though if that's what you are using Jynx for, than you need to rework your tactics. Honestly, Nasty Plot and Lovely Kiss is what makes Jynx usable. There are much better Nasty Plot abusers (Azelf, Porygon-Z, Ninetales, Mew, Slowking, Houndoom, Shiftry, Honchkrow, Lucario, Zoroark, even Pikachu are some examples) and superior status spreaders (Whimsicott, Breloom, Sableye). For the combo, put on a pair of sunglasses and hope that that's what you need to not go blind from Jynx's hideous appearance as you send it into battle.