Double Team is frowned upon by all who battle competitively. If you're going to be using such an Umbreon ingame, then go ahead; the AI certainly does. But you will be loathed if you bring it into a competitive context, at least by those who are serious about battling.
That said, I'd put Baton Pass over Double Team for competitive play, since you can pass the Mean Look. BTW, Heracross owns you no matter what unless you get it with Confuse Ray. Unless you have Curse as well, Heracross with either Close Combat or Megahorn will OHKO you nearly 100% of the time. Toxic only helps it (since it has Guts).
Jumpluff is awesome, even better than Umbreon in some cases. I have one that has worked very well for me:
Jumpluff @ Leftovers
EV's: 6 HP // 252 Sp. Atk // 252 Spd
Timid Nature (+Spd, -Atk)
Trait: Chlorophyll
~ Sleep Powder
~ Substitute
~ Leech Seed
~ Grass Knot
Of course, this set has several problems, the main one being that Leech Seed (and Grass Knot for that matter) won't do anything to Grass-types. Also, Sleep Powder, as useful as it is, has a somewhat dismal 75 accuracy...for that reason, it might be advisable to use Wide Lens instead of Leftovers. Additionally, you might consider Focus Sash to guard against Mamoswine/Donphan/Weavile Ice Punch and Ice Shard attacks. Either way, Sleep Powder is absolutely necessary seeing as how Jumpluff is one of the faster sleepers in the game.
