Jynx

Jynx has an excellent base 115 Special Attack stat and decent Speed and Special Defense stats of 95. From this information, Jynx may look like a great sweeper, but it is held back by a horrible base 35 Defense stat. This makes it extremely vulnerable to almost any physical attack coming its way, especially to the common Sucker Punch to which it has an unfortunate weakness. Its low HP stat doesn't help it either. On top of that, Jynx has always been overshadowed by other Psychic-type Pokemon such as Alakazam, even with its great Special Attack stat, and this generation is no different. UU's newest additions bring about even more Psychic-type Pokemon that outclass Jynx in some way, including Mew and Azelf. Both are faster than Jynx, while Mew is bulkier, and Azelf hits much harder. Jynx is weak to Stealth Rock as well, but it has some things up its sleeve that the aforementioned Pokemon don't: Lovely Kiss, a sleep-inducing move. With Lovely Kiss, Jynx has a much easier time setting up Nasty Plot or Calm Mind while its opponent is sleeping, making it a great late-game sweeper.

Jynx also received a new ability this generation: Dry Skin. With Dry Skin, Jynx receives an immunity to Water-type moves, recovering HP if hit by one. This makes it a great counter to Slowbro and some variants of Suicune, easily stopping their attempts at doing much back to it with Taunt. Dry Skin also restores HP in rain, which is great for Jynx. Even the ability's debilitating effects don't matter much, since many Fire-type moves already KO Jynx, and sun is uncommon in UU.