Pokemon: Hitmonchan
Name: Agilichan
-Move 1: Agility
-Move 2: Stone Edge / Rock Slide
-Move 3: Close Combat
-Move 4: (See notes)
Item: Life Orb / Expert Belt / Focus Sash
Nature: Adamant
Ability: Iron Fist
EVs: 120 HP/252 Atk/136 Spd
The fourth move is extremely tough to choose from, so I'm laying them down:
I tried a Hitmonchan like that in Advance, running a Liechi Berry, Rock Slide, Sky Upper, and Bulk Up. That being said, Bulk Up is a viable move for the fourth slot if you think you can pull one off. Liechi berry is useful since Hitmonchan usually goes into critical after one hit... so you'd use Agility, get hit, and have Liechi activate. Bulk Up can be used if you predict a switch, but have the guts to try to sacrifice an attack to power up.
Pokemon: Bibarel
Name: Duster
-Move 1: Superpower
-Move 2: Pluck
-Move 3: Blizzard/Ice Beam
-Move 4: Thunder/Thunderbolt
Item: Choice Scarf
Nature: Rash/Naive
Ability: Unaware
EVs: 252 Speed, split the remainder into Attack and S Attack
Gimmicky, theoretical, untested, and no calculations. That being said, let's move on to the basis.
Choice Scarf + Unaware allows Bibarel to outspeed a LOT of things. With Rash, it hits 361 speed; with Naive, 397. This means it can hurt/kill Tyranitar, Weavile, Heracross, Breloom, Infernape, Garchomp, Dragonite, Salamence, Gyarados, Rayquaza, Skarmory, Hippowdon, Magnezone, and Tangrowth. Note that I have not done any calculations (and I would truly appreciate it if someone could lead me to a site where I could try D/P damage calcs), and most of the Pokemon on said list are hurt, not killed.
Bibarel can switch into Weavile's Ice Shard, resist it, and OHKO with Superpower presuming Bibarel is faster (Naive). Bibarel can also switch into Gyarados' Waterfall or Ice Fang and Thunder it for good damage, though the KO is unlikely. I THINK Bibarel can OHKO the Dragons with Blizzard, and will always be faster than them, even if it cannot switch into any of them. Heracross and Breloom MAY be taken out by Pluck, but would most likely need residual damage. Infernape won't be taken out by Pluck without Close Combat defense drops or residual damage (which, actually, is common). Skarmory, Hippowdon, Magnezone, and Tangrowth are unlikely to ever be taken down by Bibarel, but Bibarel can at least deal fair damage to them.
Other options include Grass Knot (for Swampert), Waterfall (for Infernape and flinch hax), Thunderwave, Toxic, and Yawn. Status moves, however, aren't too effective when there are so many other Pokemon who can do them better.
Bibarel remains pathetically weak, but there's a CHANCE it may be able to take down a good portion of OU's powerhouse sweepers due to its speed + Unaware and the surprise factor. Note that the only Pokemon on the list that Bibarel has a chance to switch in on are Weavile (Ice Shard), Gyarados (Waterfall and Ice Fang), and Skarmory.