Let's just jump right in.
Jirachi @ Choice Scarf
Ability: Serene Grace
Nature: Jolly
80 HP, 252 Attack, 176 Speed
-Iron Head
-Trick
-U-turn
-Stealth Rock
Trick can mess up the bulkier leads that suddenly become useless with a Choice Scarf. There's a 60% chance of Flinching suicide leads and Machamp leads to death. U-turn it there to get out if there's a bad match-up or just to do some damage while switching out after Rachi has done its job.
Scizor @ Choice Band
Ability: Technician
Nature: Jolly
244 HP, 252 Attack, 12 Speed
-Bullet Punch
-U-turn
-Superpower
-Pursuit
A good check to most set-up sweepers with Technician-boosted Choice Band Bullet Punch. U-turn out when an opponent is forced to switch to do significant damage to just about everything, or just Pursuit if it's more important to hit the fleeing foe. Superpower to catch things like Heatran and Magnezone on the switch-in.
Flygon @ Choice Band
Ability: Levitate
Nature: Adamant
4 HP, 252 Attack, 252 Speed
-Outrage
-Earthquake
-U-turn
-Stone Edge
Choice Band for surprise effect and to just nail everything hard. STAB Earthquake heavily damages everything that doesn't resist it or isn't immune. Outrage for secondary STAB and sheer power. U-turn for scouting and hit-and-run damage. Stone Edge to pick off things like Gyarados that it can't touch otherwise.
Rotom-H @ Leftovers
Ability: Levitate
Nature: Bold
252 HP, 168 Defense, 88 Speed
-Thunderbolt
-Shadow Ball
-Pain Split
-Will-O-Wisp
A good check to Gyarados and most physical attackers. Will-O-Wisp cripples a lot of physical sweepers in the OU metagame. Thunderbolt for Gyarados and just a strong STAB. Shadow Ball for other Rotom and things immune to Thunderbolt. Pain Split for recovery.
Tyranitar @ Leftovers
Ability: Sand Stream
Nature: Careful
252 HP, 40 Defense, 216 Special Defense
-Curse
-Rest
-Sleep Talk
-Payback
I felt like testing out a Cure Tyranitar, and found out that a lot of teams aren't prepared for it and even struggle with it. Its natural bulk with the given EV spread allows it to set up on a lot of common Pokemon in OU.
Gyarados @ Leftovers
Ability: Intimidate
Nature: Impish
156 HP, 72 Attack, 96 Defense, 184 Speed
-Dragon Dance
-Taunt
-Waterfall
-Stone Edge
Taunt allows it to set up on a lot of stall Pokemon that suddenly find themselves unable to set up or touch Gyarados. After a few Dances it can run through a team.

Jirachi @ Choice Scarf
Ability: Serene Grace
Nature: Jolly
80 HP, 252 Attack, 176 Speed
-Iron Head
-Trick
-U-turn
-Stealth Rock
Trick can mess up the bulkier leads that suddenly become useless with a Choice Scarf. There's a 60% chance of Flinching suicide leads and Machamp leads to death. U-turn it there to get out if there's a bad match-up or just to do some damage while switching out after Rachi has done its job.

Scizor @ Choice Band
Ability: Technician
Nature: Jolly
244 HP, 252 Attack, 12 Speed
-Bullet Punch
-U-turn
-Superpower
-Pursuit
A good check to most set-up sweepers with Technician-boosted Choice Band Bullet Punch. U-turn out when an opponent is forced to switch to do significant damage to just about everything, or just Pursuit if it's more important to hit the fleeing foe. Superpower to catch things like Heatran and Magnezone on the switch-in.

Flygon @ Choice Band
Ability: Levitate
Nature: Adamant
4 HP, 252 Attack, 252 Speed
-Outrage
-Earthquake
-U-turn
-Stone Edge
Choice Band for surprise effect and to just nail everything hard. STAB Earthquake heavily damages everything that doesn't resist it or isn't immune. Outrage for secondary STAB and sheer power. U-turn for scouting and hit-and-run damage. Stone Edge to pick off things like Gyarados that it can't touch otherwise.

Rotom-H @ Leftovers
Ability: Levitate
Nature: Bold
252 HP, 168 Defense, 88 Speed
-Thunderbolt
-Shadow Ball
-Pain Split
-Will-O-Wisp
A good check to Gyarados and most physical attackers. Will-O-Wisp cripples a lot of physical sweepers in the OU metagame. Thunderbolt for Gyarados and just a strong STAB. Shadow Ball for other Rotom and things immune to Thunderbolt. Pain Split for recovery.

Tyranitar @ Leftovers
Ability: Sand Stream
Nature: Careful
252 HP, 40 Defense, 216 Special Defense
-Curse
-Rest
-Sleep Talk
-Payback
I felt like testing out a Cure Tyranitar, and found out that a lot of teams aren't prepared for it and even struggle with it. Its natural bulk with the given EV spread allows it to set up on a lot of common Pokemon in OU.

Gyarados @ Leftovers
Ability: Intimidate
Nature: Impish
156 HP, 72 Attack, 96 Defense, 184 Speed
-Dragon Dance
-Taunt
-Waterfall
-Stone Edge
Taunt allows it to set up on a lot of stall Pokemon that suddenly find themselves unable to set up or touch Gyarados. After a few Dances it can run through a team.