Tyranitar, pseudo-legendary of the 2nd generation, one of the premier Sandstorm setters and terror of many teams. Tyranitar has been a nightmare since its inception, and looks to remain that way, even into the future.
Tyrant in the Sand (Doubles/VGC)
Tyranitar
Ability: Sandstream
Item: Smooth Rock/Air Balloon
-Rock Slide
-Crunch/Snarl/Assurance
-Breaking Swipe/Earthquake
-Protect
Nature: Adamant (+ATK, -SATK) OR Brave (+ATK -SPE)
EVs: 84 HP/204 ATK/4 DEF/0/12 SDEF/204 SPE OR 180 HP/252 ATK/76 SATK
Tyranitar is a terror in doubles having a wide and varied moveset and a myriad of support option. Of most significant note is it's ability Sand Stream. Tyranitar remains one of the best users of the ability, synergizing with Sandstorm, getting a sizeable SDEF boost and getting chip damage on opponents, allowing it to reach for KOs that would otherwise be out of reach. This, on top of fueling other abilities like Excadrill's Sand Rush, Rhyperior's SDEF boost and countering other weathers like Torkoal's Drought and Pelipper's Drizzle can immediately reverse momentum back to your side (note that Torkoal is naturally slower than Tyranitar, so if they are sent out at the same time, Torkoal's Drought will take precedence).
Rock Slide is the STAB of choice, hitting both targets and having a decent flinch chance on the off chance that Tyranitar outpspeeds the opposition (or out slows under trick room). For your secondary STAB you have a few choices. Crunch is the reliable single target STAB of Choice, hitting hard with no drawbacks. Assurance is an interesting choice, for if Tyranitar is paired with a faster Pokémon that can hit both opponents with a spread move or if you want to focus fire, Assurance becomes a massive base 120 Dark move that will likely take out anything that doesn't resist/extremely bulky. However, focus firing can be risky if your opponent decides to protect, so keep that in mind. Snarl while weak (and requiring different investment), but as a STAB spread move that reduces SATK, it certainly has its merits.
For coverage moves, Earthquake is as always a fantastic option hitting a wide variety of types hard for massive damage, while Breaking Swipe is an excellent counterpart to Snarl, being physical and reducing both target's ATK, though being Dragon typed means relatively poor coverage and no selled by fairies.
Protect is fantastic for Doubles, and especially Tyranitar enabling it to get a bit more chip damage with Sandstorm, as well as blocking focus fire attempts on the relatively bulky Tyranitar. Additionally many of Sandstorm's best abusers (Excadrill, Rhyperior) like Earthquake, which Tyranitar does not like eating.
For items, Smooth Rock enables a longer Sandstorm while Air Balloon enables both Tyranitar and its earthquaking partner to attack as well as blocking other Ground type assaults.