I was playing Suspect and looking for a good Encore user when I came across this (also usable in OU):
Jumpluff @ Leftovers
Nature / Ability: Timid / Chlorophyll
EVs: 188 Def / 68 SpD / 252 Spe
~ Encore
~ Leech Seed
~ Substitute
~ Hidden Power Flying/Aerial Ace (with Jolly nature)
This set is almost the same as the SubSeed set on the Analysis. However, the way this set plays is a little different. While the analysis suggests the option of scrapping Encore for Aerial Ace, this set opts to give up Sleep Powder for Hidden Power Flying instead. Sleep Powder is limited by Sleep Clause, and only has 75% accuracy. HP Flying does a surprisingly large amount of damage against many Fighting and Grass types, even without any EV investment. By using HP Flying instead of Sleep Powder, Jumpluff gains the ability to counter a few Fighting type Pokemon and finds a niche as one of the best SubSeeders and Encore users in the game.
Thanks to Jumpluff's Ground immunity, 4x resist to Grass, resistances to Fighting and Water, and relative bulk, it has a fairly easy time switching into attacks. From there, you have the option of Encoring their useless move or Substituting. People are often surprised to see a NU Pokemon in OU and forget that Jumpluff is one of the fastest Encore users and get locked into Substitute or Earthquake, giving Jumpluff a free setup.
Aerial Ace is listed as another option for dealing with Grass Pokemon who are more specially defensive, like Roserade. You can still put the hurt on popular Fighting types, but the problem lies in the fact that Pokemon like Shaymin and Roserade tend to carry HP Ice or Fire specifically to deal with other Grass types, so it usually isn't worth it to stay in.
As a SubSeeder, Jumpluff naturally tears through Stall. Blissey only does 39.2%-46.7% with Flamethrower and Jumpluff loves the amount of HP it gets to drain. Encore means free switch ins on predicted Subs, Calm Minds, Curses, and Stockpiles. Outside of regular SubSeed duties, this set completely counters both the popular SubSeed and SubPunch Breloom sets, as long as you have something to absorb the Sleep (preferably something that can outspeed Breloom and survive a Focus Punch, in case it decides to Sub). It can even switch into a Grass Knot or Close Combat from Infernape and Encore or Aerial Ace, respectively. You may want to throw a few EVs into SpA for that, though.
Hidden Power vs. SubSeed Breloom: 87.5%-105%
Hidden Power vs. SubPunch Breloom: 1HKO
Hidden Power vs. 0/0 Heracross: 65.1-77.1%
+1 Adamant 252 Atk EVs Heracross's Close Combat vs. Jumpluff: 56.7%-67%
Hidden Power vs. 0/0 -1 Heracross: 1HKO
Naive 252 Atk EVs Life Orb Infernape's Close Combat vs. Jumpluff: 39.5%-46.7%
Hidden Power vs. -1 0/0 Naive Infernape: 70.3-84% <- a 52.6% chance of a 1hko after Stealth Rock and LO recoil; also keep in mind that Infernape rarely gets a switch in unharmed.
Heatran is the perfect partner for this Jumpluff, as it lures Ground, Fighting, Water attacks while providing resists to Fire and Ice attacks, and deals with the fellow Grass types that give it trouble with Fire Blast. Swampert and other Bulky Waters are also good to pair with this Jumpluff, as they lures Grass Knots and resists incoming Fire attacks from faster Pokemon. Jumpluff also benefits greatly from Stealth Rock support. Liquid Ooze Tentacruel is also a problem for Jumpluff, so make sure you have something to deal with that.
SubSeed is fairly rare in OU thanks to the offensive nature of the metagame, but this set worked pretty well when I was laddering on my test account with a rating around 1300. If Salamence gets banned, this set will become even more powerful, due to an increase in the use of Fighting types.