P(n) = 1 - (1 - P(1))^n
Abilities: Chlorophyll, Leaf Guard, Infiltrator (HA)
HP - 75
Attack - 55
Defense - 70
Special Attack - 55
Special Defense - 95
Speed - 110
Jumpluff has become my absolute favorite VGC2014-legal Pokemon. The reason: It is so anti-metagame its not even funny. It has access to an obscene number of good support moves, including Sleep Powder, Stun Spore, Rage Powder, Encore, Protect, Cotton Spore, Worry Seed, Memento, Toxic, Aromatherapy, and Helping Hand. It is obscenely fast, outspeeding most common sweepers. It has access to Chlorophyll (to make it even more obscenely fast when in the company of Charizard-Y), as well as Infiltrator to bypass the ever-common Substitute and Safeguard. It also had its special defense stat boosted ever so slightly from BW to XY.
Its only real weaknesses are an inability to stand up to Talonflame without a Coba Berry, it being taunt bait, and being 4x weak to Ice. Its physical defenses aren't anything special either.
This is the set I run the most, and it is just annoying for opponents to face.
Jumpluff @ Coba Berry
EVs: 252 HP / 60 Def / 196 Speed
EVs + Coba Berry are designed to always survive a Choice Band Talonflame's Brave Bird, and to always outspeed an unboosted Garchomp. Put opponents to sleep with Sleep Powder (even Safeguard doesn't protect you thanks to Infiltrator), then use Helping Hand to help your opponent to sweep. If your opponent decides to Protect, go with the Encore if they are slower than Jumpluff. It is unfortunately bait for Fire and Ice attacks, and Sleep Powder does have an annoying habit of missing. Also opposing Grass types are immune to Sleep Powder. One very nice thing about Sleep Powder is that King's Shield doesn't block it, which means those pesky Dark Void Smeargles who open with King's Shield will likely be put to sleep.
Coba Berry can be swapped with any number of items, including Yache Berry, Occa Berry, Charti Berry, Focus Sash, or Mental Herb, to prevent specific attacks from becoming OHKOs.
Encore is really the only move that is flexible. It can be subbed with Giga Drain or Bounce to keep it from being complete Taunt bait, or it can be swapped with any desired support move of choice.