Indeed, Jolly is the way. The EVs vary, 252 in Spd is a given, and then it's your call. You can put the rest into Atk if you use U-Turn, or Sp.Def/Def. Even HP for better Substitutes. I'd go for Spd and HP.
Some variants:
Jumpluff @ Leftovers / BrightPowder (is it allowed?)
Ability: Chlorophyll
Jolly
- Substitute
- Leech Seed
- Sleep Powder
- U-Turn / Aromatherapy
Jumpluff @ Leftovers / Light Clay
Ability: Chlorophyll
Jolly
- Stun Spore
- Leech Seed
- Encore
- Reflect / Substitute
Bring it out in Sunny Day and it'll be a beast (with a maximum of 700 Speed).
F