Evil shadows are on Wobbuffet's tail this iteration of OU. For starters, accumulating passive damage in the form of stacked entry hazards, status afflictions, and Sandstorm has become the prevalent strategy and Wobbuffet is vulnerable to all of these things. Second, although fresh from the Ubers tier, the attackers in BW OU hit just as hard with their weather-assisted Choice attacks and as such Wobbuffet cannot repeatedly switch into or reliably defeat the Pokemon it was seemingly meant to counter. Taunt users such as Gliscor and Mew have also become commonplace, and Wobbuffet cannot touch them. Third, the game's very mechanics have been changed to mitigate Wobbuffet's properties. Because of Team Preview, your opponent knows from the first turn that you brought a Wobbuffet, and can act accordingly; futhermore, Encore's duration has been changed from a variable 3-7 to a static 3 turn duration which limits the extent of Wobbuffet's support for the team. And last but not the least, while a mono-Psychic typing doesn't mean a total lack of useful defensive properties, combine its lack of recovery options or an ability that protects it from Spikes damage with the fact that it needs to maintain a high amount of HP to be useful and you have a Pokemon that's possibly only coming in on a double-switch, revenge kill, or resisted Choice attack.
So is all hope lost for our favorite sentient punching bag? That's the way it is- there are specific offensive builds that heavily appreciate Encore's ability to set up a sweeper or eliminate particularly annoying Scarfers. But if you need a Shadow Tag abuser that removes Keldeo and such from the game, please consider using Gothitelle.
name: Oh No, It's Wobbuffet!
move 1: Counter
move 2: Mirror Coat
move 3: Encore
move 4: Safeguard/ Destiny Bond
ability: Shadow Tag
EVs: (to be decided, I'm thinking 252 HP/ 252 SpDef/ 4 Def. This avoids the OHKO from Specs Keldeo in Rain after rocks 87.5% of the time, and can still deal with Specs Tornadus, Specs Latios, Scarf Lando-T locked on Earthquake, and Terrakion/ Mienshao locked on Fighting moves)
-CounterCoat is standard fare
-Encore allows it to harass Amoonguss, Ferrothorn, Reuniclus, and Slowking, as well as set-up a weak attacker for a kill or as set-up bait for another Pokemon if it chooses not to attack
-Encore followed by Safeguard allows it to lock someone on a status move then give an attacker a free switch-in
Checks and Counters
-technically none and Shed Shell is less popular now
-Taunt Mew/ Gliscor/ Skarmory