Outside of the NU metagame, there's really nothing Plusle can do that can't be done better by something else. Jolteon can Baton Pass Substitutes, Pikachu / Raichu can Substitute + Encore, etc. In NU, though, Plusle combines all of these and is the best special threat that doesn't need some kind of weather set up. It's something people should keep in mind when making an NU team, both as an option for a member and to make sure you carry a counter. Definitely a recommended NU Pokémon.
Plusle should not be venturing outside of NU, but inside that safe zone it shines as one of the best special sweepers available. The last move is also up to personal preference. You can Baton Pass around Substitutes, or Encore a Leech Seed or Toxic once safely behind your Substitute. This makes a good starter (especially the Baton Pass version) as its counters are rarely starters themselves, so you can safely get your Substitute up and follow your plan.
The IVs given are for Hidden Power Ice. Hidden Power Grass hits Whiscash on its 4x weakness, but Hidden Power Ice hits Grass types.
Use Modest with Agility, but Substitute can use either nature. Petaya Berry goes with Substitute, Leftovers goes with Agility.
Fake Tears works best if you have something like Spikes Roselia on your team to prevent them from just switching out of it. Substitute lets you activate your Petaya Berry and helps scout out switches caused by Fake Tears / Encore. It also lets you Substitute against a status move or a stat up, then Encore them.
Light Screen and Wish are available to make it more of a team player, but are probably better off on its counterpart Minun, who has more Special Defense to work with. Toxic and Thunder Wave are available to status when you can't think of anything better to do.
Max Speed and Special Attack. Timid will allow you to beat Jolly Pidgeot and Adamant Raticate, but you won't be OHKOing most Whiscash with Hidden Power Grass. Modest will give you a chance with more power.
Checks and Counters
UU: Manectric and Electabuzz can abuse their resistance to Thunderbolt and greater stats to simply overpower Plusle. Quagsire stops those without Hidden Power Grass, and Gligar sets up on those without Hidden Power Ice. Kangaskhan also has the HP to come in and kill it / scare it off. Cradily walls Plusle even easier than it walls most Electrics, which is saying a lot. Basically, anything not weak to Electric and not 4x weak to Plusle’ Hidden Power is a decent counter if it has any sort of Special Defense stat.
NU: Sunflora, Parasect, and Roselia can stop the Hidden Power Grass variant. Whiscash can stop you if you have Hidden Power Ice. Trapinch can potentially survive anything Plusle uses against it, but Plusle can always threaten Petaya. Swalot and Kecleon will make you switch a few times, but both take a decent hit from Thunderbolt. Wigglytuff and Minun can both come in, Light Screen, and Wish themselves better.