I can't believe no one has posted this yet. It just goes to show how uncommon it is nowadays. I give you one of my all time favorite ubers Pokemon:
Shaymin Sky@ leftovers
Ability: Serene Grace
Nature: Timid (+spe -att)
EV's: 252 spe/ 244 hp/ 12 sp att
Leech Seed
Substitute
Air Slash
Seed Flare
Once he gets going, he is EXTREMELY hard to stop. SubSeed really adds up, and as the only grass types you see are Arceus and Ferrothorn, you won't have much trouble getting them up. Air slash brings a massive 60% flinch rate. Seed flare helps break down even the bulkiest special walls because of its great defense drop rate. This thing is the definition of annoying.
This isn't a joke set. This is jumpluff in ou:
Jumpluff@ leftovers
Ability: Chlorophyll
Nature: Jolly (+spe -sp att)
EV's: 252 spe/ 232 hp/ 24 att
U-turn
Leech Seed
Encore
Sleep Powder/ Stun Spore
With sun support, jumpluff becomes INSANELY fast. Only a select few scarfed Pokemon outspeed him. He fits extremely well on sun teams as he is immune to the ground type moves your Heatran, Ninetales, etc. all hate. He can come in on a ground or water move and use encore, which is going to force a lot of switches. He can then use leech seed, stun spore, or sleep powder on the switch in. It can then u-turn into the appropriate Pokemon to deal with said switch in. Jumpluff destroys momentum, while grabbing some for you. Leech seed can also easily be passed on to Pokemon that will better take advantage of it, such as CM Reuniclus.
Well, I hope you liked my annoying grass types. :D