Use

Terrakion @ Salac Berry/Rock Gem
Trait: Justified
EVs: 4 HP / 252 Atk / 252 Spd
Nature:Jolly
- Swords Dance
- Close Combat
- Stone Edge
- Substitute
Role: Physical Sweeper/Wall Breaker/Late Game Cleaner
What It Does:Probably the best physical sweeper in the OU metagame.Due to it's great offensive presence it can easily force a lot of switches getting a free turn where you SD or Sub.Then using Sub as you're protection from revenge killing and status (use SD first only when you can predict right),set up and sweep.If you're using Salac Berry,the trick is to keep subing on a faster mon(but slower when terrak is at +1 spd) till Salac berry is activated.Then you'll be faster and you can set SD as you're Sub is broken.Then start your sweep.However,priority users and faster threats should be eliminated for a clean sweep.You can also cause a lot of damage with the use of Sub when you're not in good position to activate salac berry.Rock Gem is an alternative item suited for wallbreaking OHKOing Gliscor,Def Celebi and Def Amoongus at +2 with Stone Edge and things like OHKOing Landorus after Rocks at +0.
Good Teammates: Tyranitar is good teammate who can provide Sand making it easier to set up and making it harder to break the sub for weak defensive mons.It also gives you weather control for dealing with annoying chloro sweepers.TTar can also eliminate Scarf Latios.Dragon Types such as Salamence,Dragonite and Latios make good partners due to their nice offensive and defensive synergy.Gothitelle is a cool partner thanks it ability to trap and kill physical walls like Gliscor and Hippodawn who give terrakion some trouble and scarf Versions can reliably beat Breloom,one of terrakions biggest enemy.
What Counters It: Not much thanks to terrakion's incredible dual STABs with high attack stats.But Hippodawn,Gliscor and Physically Defensive Celebi can tank a +2 hit and hit back with STAB super effective attacks.But the later two much be weary of Rock Gem.None of them can OHKO terrak without prior damage so you can go for an additional SD if you're at full health but don't risk Twave paralysis on Celebi.Scizor and Breloom can revenge kill Terrakion with their prority attacks.Scarf Latios can also revenge kill it.And anything faster with strong/super effective attacks can KO terrak if it doesn't have the speed boost like Latias,Genger,Starmie,Tornadus-T etc.Sub helps against revenge killing.
Any Additional Info: Use this guy,He's awesome!