- If allied with a Pokemon with Plus or Minus, the wielder's Special Attack increases by 50%.
Level 100 Statistics (see level 5, 50, 100)
Plusle is outclassed by Raichu, but it offers one thing over it and one thing only: Baton Pass. When the going gets rough, Plusle at least has the option to keep up momentum and pass its +2 Special Attack to a teammate that can hopefully maintain its sweep. Unfortunately, Volbeat also sports the ability to pass Special Attack boosts, and a +3 one with priority at that. Luckily, Plusle hits harder and so is less of a liability should all else fail.
Plusle will have a tough time setting up a Nasty Plot, but if you can manage to get it in on a Water-type, you can maybe pull it off. From there, blast away with Thunderbolt and Hidden Power until Plusle just can't blast anymore and pass the Nasty Plot boost to a teammate. While Plusle is pretty fast for NU, it has some serious trouble with Choice Scarf users, predominantly Primeape, since it can't withstand any of its attacks and won't be able to pass on its Nasty Plot boost. If at all possible, try to eliminate the opponent's Choice Scarf user before bringing in Plusle.
Any Pokemon with a decent Special Attack stat will enjoy a +2 boost, but the trick is to pass to something that will both be able to weather the incoming hit and outspeed the opponent once it's in. Charizard, Articuno, and Rotom-S all usually can do this and are immune to Ground-type attacks as well. Tangela and Exeggutor resist Ground-type attacks and are very physically bulky, but are pretty slow, meaning they'll likely have to take two hits before attacking.
Encore can provide Plusle with more set up opportunities, but Baton Pass is about the only thing it has over Raichu, so that's the niche it needs to provide. Encore can go over Hidden Power Ice, but mono-Electric coverage is just asking for trouble down the line. Any support set or a more dedicated Baton Pass set is better left to Minun.
Checks and Counters
Piloswine is a good immediate answer to Plusle, and it's strong enough to threaten most of the Pokemon that Plusle would generally want to Baton Pass to as well. There's actually a small amount of Pokemon that won't mind taking a +2 Thunderbolt or Hidden Power Ice, but most that resist Thunderbolt still make a good answer, particularly Grass-types like Roselia. Revenge killing is the best way to both eliminate Plusle and any potential threat it could Baton Pass to. Choice Scarf Primeape, Zebstrika, Tauros, and Scolipede are all decent answers. Priority from Zangoose also works well.