Wynaut hasn't changed a bit since DPP; its small yet perfectly suited movepool remains the same, along with its always-useful role in helping set-up Pokemon. Wynaut did gain a boost in the introduction of the Eviolite, which only adds to its durability. With so many new threats to stop and support, Wynaut remains a very good Pokemon in this generation.
Wynaut retains the same niche it had last generation, as its impressive ability to dispose of Choice-locked attackers is invaluable to many Pokemon. There are also many strong attackers which can blast holes through teams that Wynaut traps and KOes, such as Snover. It also has the ability to get rid of slower attackers and Encore set-up Pokemon, meaning Wynaut will almost always be of use in every game.
Wynaut's movepool, while only consisting of eight moves, is perfectly suited for its job. Shadow Tag lets it trap opposing Pokemon so that they can't switch out. If the Pokemon is locked into a physical attack, Counter will dispose of it, unless Wynaut is KOed, which is unlikely considering its massive HP stat and respectable defenses. Mirror Coat bounces back special attacks. However, the crux of Wynaut's viability lies in the move Encore. Encore lets it force attackers to repeat a move, meaning you can either switch in a Pokemon that takes little damage from the attack and set up, or just KO it with Counter or Mirror Coat. If your opponent tries to set up on Wynaut, Encore lets you switch in a Pokemon to set up on it while your opponent is locked into a move for three turns.Team Options & Additional Comments >>>
As mentioned several times earlier, Wynaut's movepool is slightly lacking in quantity. All the viable moves have been mentioned already. Splash is useless, unless you really want to rub your victory in your opponent's face. If that's the case you're better off using Magikarp or Hoppip, however. Charm on the other hand is plausible, but Tickle tends to be better since it not only lowers Attack but Defense as well, having added utility.
The amount of Speed Wynaut runs is up to the user. Wynaut's Speed, with a neutral nature, can hover anywhere between 8 and 12. Wynaut needs Speed to outrun walls, and lock them into an attack. Wynaut outspeeds Ferroseed with no investment, and you can choose to go with the lowest Speed possible to take as little damage from Gyro Ball as possible. 172 Speed is needed to outspeed no Speed Frillish, but this really takes away from its defenses. 12 Speed EVs are probably the optimal investment, a small amount to outspeed walls, but not enough to impact defenses. If you would like Wynaut to outspeed Hippopotas, 92 Speed EVs are needed.
Checks and Counters
There is no real counter to Wynaut, as, barring a few exceptions, nothing can switch in. However there are several ways to dispose of Wynaut. After Wynaut faints a Pokemon, a strong Pursuiter, such as Cranidos or Munchlax, can come in and knock it out. Common Choice-locked Pokemon which are often trapped by Wynaut might opt to run a set using an Expert Belt or Oran Berry to trick Wynaut into using a reflecting move while they boost up and then KO it. However, this is a very specialized approach which will rarely see use otherwise. Also, as Wynaut's only way of doing damage is reflecting an attack, specially attacking Dark-types and physical Ghost-types, such as Houndour and Duskull respectively, are immune to Wynaut's attacks. Other specific Pokemon who threaten Wynaut are Gastly and Scraggy. Taunt is an absolute killer to Wynaut, since once Taunted it can only use Counter and Mirror Coat. Lastly, anything with Volt Switch, U-turn, or a Shed Shell will avoid capture, effectively countering Wynaut as it can't do its job. Be warned, however, that if Wynaut uses Mirror Coat on Volt Switch or Counter on U-turn, the Pokemon that switches in will take damage.
The Custap Berry is yet to be released from the Dream World, but when it is, a Custap Berry + Destiny Bond set will be viable. It will allow Wynaut to KO one Pokemon with either Counter or Mirror Coat, then Destiny Bond the next before they can attack, and usually net two kills per match.