My OU team is by no means terrible, and I get my fair share of wins, but I was hoping for some aid to patch up some holes in my team, which is:
Haxorus
Starmie
Reuniclus
Infernape
Metagross
Tyranitar
In depth:
Haxorus@Focus Sash
ability: Mold Breaker
EVs: 252 atk, 252 spe, 4 hp
nature: Lonely
Outrage
Brick Break
Earthquake
Dragon Dance
Haxorus is a defensive pokemon's worst nightmare, and after a DD, it is unstopable without a priority move, or Jolteon with HP ice. While not a favorable switch in, sending in haxorus after a partner faints, taking a hit on the first turn, surviving thanks to focus sash, getting a DD, and then sweeping has proven very reliable.
However, Haxorus has to especially watch out for priority moves, weather damage, any statuses, entry hazards, and blazing fast pokemon like jolteon, weavile, and aerodactyl.
Starmie@Expert Belt
Ability:Natural Cure
EVs: 252 Spatk, 252 spe, 4 hp
Nature:Timid
Surf
Psyshock
Thunderbolt
Ice Beam
Starmie is a killer, outspeeding almost everything and hitting tons of pokemon for super effective damage, and everything but ferrothorn for neutral. With classic boltbeam, that expert belt gives starmie that extra little push, without the life orb recoil, that I tried at first before forgoing it for expert belt. Also psyshock for beating up blissey, snorlax, etc.
starmie has to look out for zoroark, jolteon, sceptile, and scarfed heracross. because they all have potential to STAB OHKO starmie. Also dealing with anything that has sucker punch sucks. Gengar has posed a problem as well, but not as seriously as the other mentioned pokemon.
Reuniclus@Leftovers
Ability:Magic Guard
EVs: 192 HP, 64 Def, 252 Spatk
Nature:modest
Calm Mind
Recover
Psyshock
Focus Blast
Reuniclus has a few tricks up its sleeve, being able to set up on nearly anything but tyranitar, gengar, and chandelure by spamming calm mind then recover, it is also set up to kill popular switch ins, taking out special walls with psyshock, and dark types with focus blast.
as i mentioned, chandelure, gengar, and tyranitar pose huge threats to reuniclus. also it can't do anything to other reuniclus, or cresselia. scizor is also a real pain with u turn/bug bite.
Infernape@choice scarf
Ability: Blaze
EVs:252 atk, 252 spe, 4 HP
Nature:naive
Flare Blitz
Earthquake
Close Combat
Stone Edge
Infernape's job is to patch up the holes in my team, and to revenge kill. He outspeeds Jolteon and sceptile, kills ferrothorn and pesky bug/steel types, and can help out with common threats to other members of my team, like aforementioned jolteon, sceptile, tyranitar, and chandelure. He also does a great job handling pokemon like the musketeers, the genies, the bird trio, blissey, snorlax, and the list goes on.
All that being said, infernape is fragile, and i consider it lucky to survive even one hit. Dragonite and the lati's murder me, and any ferrothorn/chandelure combo, has its way with me after chandelure switches into a flare blitz with flash fire. dealing with ghost types suck, hippowdon and gliscor wall me all day, but that's given.
Metagross@Air Balloon
Ability:Clear Body
EVs:252 HP, 252 Atk, 4 Spe
Nature: Adamant
Meteor Mash
Bullet Punch
Earthquake
Hammer Arm
Metagross is my tank. He also helps a bit with my desperate need for someone with a priority move. Being able to tank so many things is what make metagross great, even being able to take a flamethrower from hydreigon with a little luck. he also shares a somewhat similar role as infernape in that he destroys jolteon, sceptile, and weavile. Hammer arm nails darks and steels that might want to try to beat him.
Metagross is slow, and is somewhat reliant on his Air Baloon. Also he has serious problems hurting any bulky waters like jellicent, suicune, and milotic. Also he can't do anything against gliscor and landorus, and has some problems with Hippowdon, but has come out on top in the past by spamming earthquake.
Tyranitar@Chople Berry
Ability: Sandstream
EVs:252 HP, 252 Atk, 4 Def
Nature: Adamant
Crunch
Stone Edge
Fire Fang
Stealth Rock
Tyranitar is the newest, most unproven, most out of place pokemon on my team, since I've only been using him for about a week. He works well enough with Metagross and Reuniclus, but for haxorus to work, haxorus has to go before tyranitar sets up sandstorm. He's got some wicked STABs, stealth rock, and fire fang to beat incoming steels, and I chose fire fang over fire punch for flinching, which is like having jesus on your side when it happens. He's set up as another tank, and although he isn't always the best option depending on the team I'm facing, He does a damn good job at what he does best, mainly picking up starmie or haxorus' scraps. He can also clear the way for Reuniclus to set up, taking out reuniclus' counters.
Like any tyranitar, he's got serious trouble dealing with his wide array of weaknesses. He's also a little awkward to use, and doesn't flow as nicely as say starmie, who can usually take out opponent after opponent with out having to stop and think.
So my biggest threats are obvious, being mentioned several times, Sceptile, Jolteon, and also opposing starmie, gengar, latios/as, Gliscor, Landorus, and to a lesser extent, bulky waters, scizor, reuniclus cresselia, salamence, dragonite, and flygon. Also Slowbro kicks my ass.
Not currently in use, I have a latios, who I switched for Tyranitar, because of my inability to deal with psychic and ghosts, and my overabundance of psychic pokemon. a jellicent, a cresselia, a ferrothorn, a scizor, a skarmory, and a heatran, all of whom I would easily consider using.
Any advice about other things to watch out for, moveset or ev changes, even suggestions about using other pokemon especially those I listed above would be greatly appreciated.
Haxorus
Starmie
Reuniclus
Infernape
Metagross
Tyranitar
In depth:

Haxorus@Focus Sash
ability: Mold Breaker
EVs: 252 atk, 252 spe, 4 hp
nature: Lonely
Outrage
Brick Break
Earthquake
Dragon Dance
Haxorus is a defensive pokemon's worst nightmare, and after a DD, it is unstopable without a priority move, or Jolteon with HP ice. While not a favorable switch in, sending in haxorus after a partner faints, taking a hit on the first turn, surviving thanks to focus sash, getting a DD, and then sweeping has proven very reliable.
However, Haxorus has to especially watch out for priority moves, weather damage, any statuses, entry hazards, and blazing fast pokemon like jolteon, weavile, and aerodactyl.

Starmie@Expert Belt
Ability:Natural Cure
EVs: 252 Spatk, 252 spe, 4 hp
Nature:Timid
Surf
Psyshock
Thunderbolt
Ice Beam
Starmie is a killer, outspeeding almost everything and hitting tons of pokemon for super effective damage, and everything but ferrothorn for neutral. With classic boltbeam, that expert belt gives starmie that extra little push, without the life orb recoil, that I tried at first before forgoing it for expert belt. Also psyshock for beating up blissey, snorlax, etc.
starmie has to look out for zoroark, jolteon, sceptile, and scarfed heracross. because they all have potential to STAB OHKO starmie. Also dealing with anything that has sucker punch sucks. Gengar has posed a problem as well, but not as seriously as the other mentioned pokemon.

Reuniclus@Leftovers
Ability:Magic Guard
EVs: 192 HP, 64 Def, 252 Spatk
Nature:modest
Calm Mind
Recover
Psyshock
Focus Blast
Reuniclus has a few tricks up its sleeve, being able to set up on nearly anything but tyranitar, gengar, and chandelure by spamming calm mind then recover, it is also set up to kill popular switch ins, taking out special walls with psyshock, and dark types with focus blast.
as i mentioned, chandelure, gengar, and tyranitar pose huge threats to reuniclus. also it can't do anything to other reuniclus, or cresselia. scizor is also a real pain with u turn/bug bite.

Infernape@choice scarf
Ability: Blaze
EVs:252 atk, 252 spe, 4 HP
Nature:naive
Flare Blitz
Earthquake
Close Combat
Stone Edge
Infernape's job is to patch up the holes in my team, and to revenge kill. He outspeeds Jolteon and sceptile, kills ferrothorn and pesky bug/steel types, and can help out with common threats to other members of my team, like aforementioned jolteon, sceptile, tyranitar, and chandelure. He also does a great job handling pokemon like the musketeers, the genies, the bird trio, blissey, snorlax, and the list goes on.
All that being said, infernape is fragile, and i consider it lucky to survive even one hit. Dragonite and the lati's murder me, and any ferrothorn/chandelure combo, has its way with me after chandelure switches into a flare blitz with flash fire. dealing with ghost types suck, hippowdon and gliscor wall me all day, but that's given.

Metagross@Air Balloon
Ability:Clear Body
EVs:252 HP, 252 Atk, 4 Spe
Nature: Adamant
Meteor Mash
Bullet Punch
Earthquake
Hammer Arm
Metagross is my tank. He also helps a bit with my desperate need for someone with a priority move. Being able to tank so many things is what make metagross great, even being able to take a flamethrower from hydreigon with a little luck. he also shares a somewhat similar role as infernape in that he destroys jolteon, sceptile, and weavile. Hammer arm nails darks and steels that might want to try to beat him.
Metagross is slow, and is somewhat reliant on his Air Baloon. Also he has serious problems hurting any bulky waters like jellicent, suicune, and milotic. Also he can't do anything against gliscor and landorus, and has some problems with Hippowdon, but has come out on top in the past by spamming earthquake.

Tyranitar@Chople Berry
Ability: Sandstream
EVs:252 HP, 252 Atk, 4 Def
Nature: Adamant
Crunch
Stone Edge
Fire Fang
Stealth Rock
Tyranitar is the newest, most unproven, most out of place pokemon on my team, since I've only been using him for about a week. He works well enough with Metagross and Reuniclus, but for haxorus to work, haxorus has to go before tyranitar sets up sandstorm. He's got some wicked STABs, stealth rock, and fire fang to beat incoming steels, and I chose fire fang over fire punch for flinching, which is like having jesus on your side when it happens. He's set up as another tank, and although he isn't always the best option depending on the team I'm facing, He does a damn good job at what he does best, mainly picking up starmie or haxorus' scraps. He can also clear the way for Reuniclus to set up, taking out reuniclus' counters.
Like any tyranitar, he's got serious trouble dealing with his wide array of weaknesses. He's also a little awkward to use, and doesn't flow as nicely as say starmie, who can usually take out opponent after opponent with out having to stop and think.
So my biggest threats are obvious, being mentioned several times, Sceptile, Jolteon, and also opposing starmie, gengar, latios/as, Gliscor, Landorus, and to a lesser extent, bulky waters, scizor, reuniclus cresselia, salamence, dragonite, and flygon. Also Slowbro kicks my ass.
Not currently in use, I have a latios, who I switched for Tyranitar, because of my inability to deal with psychic and ghosts, and my overabundance of psychic pokemon. a jellicent, a cresselia, a ferrothorn, a scizor, a skarmory, and a heatran, all of whom I would easily consider using.
Any advice about other things to watch out for, moveset or ev changes, even suggestions about using other pokemon especially those I listed above would be greatly appreciated.