Well, seeing as you have Tyranitar, I'd make the focus of your team a Sandstorm team. Like 100 said, Reshiram is banned, so just take him out completely. As far as I'm aware, Garchomp isn't banned in official tournaments so if you want another Dragon type, Garchomp is a viable option. However, I'm not sure if Garchomp is legal in VGC. In any case, an ideal set for Garchomp is:
@Yache/Haban Berry
Ability: Sand Veil
Jolly (+Spe, -SAtk)
EVs: 4 HP / 252 Atk / 252 Spe
- Swords Dance
- Outrage
- Stone Edge
- Earthquake
Outrage and Earthquake give it great STAB attacks, with 180 and 150 base power each. Stone Edge is also useful for hitting things on predicted switches. Garchomp already has naturally great speed, and after just one Swords Dance, it can hit an unbelievable attack of 718.
Also, I'd drop Archeops. While it's initial attack and speed may be attractive, its ability hinders it greatly. If you want another Pokemon with a 140 Attack stat, try Conkeldurr:
@Flame Orb
Ability: Guts
Adamant (+Atk, -SAtk)
EVs: 120 HP / 252 Atk / 136 SDef
- Mach Punch
- Drain Punch
- Rock Slide
- Payback
With flame orb burning Conkeldurr from the start, you can activate Guts, which negates Burn's halve in attack, instead increasing Conkeldurr's already amazing Attack by 50%. Drain Punch will allow you to heal of damage from the burn, at the same time damaging your opponent. Rock Slide for flying types, etc. Mach Punch to quickly kill off fast threats, and Payback lets you hit Ghosts would attempt to absorb your fighting type moves.
I'd also drop Serperior, as it has generally low attacking prowess. Instead, I'd used Excadrill:
@Life Orb/Chople Berry
Ability: Sand Rush
Adamant (+Atk, -SAtk)
EVs: 60 HP / 252 Atk / 196 Spe
- Earthquake
- Rock Slide
- X-Scissor
- Protect
Sand Rush doubles Excadrill's speed in sandstorms, which Tyranitar will be providing. Life Orb gives you 30% more power in attack at the cost of 10% HP everytime you hit the opponent. Chople berry reduces the power of fighting moves, which Excadrill is weak to. Earthquake comes off at 150 base power after STAB. That's not even mentioning Excadrill's hypothetical attack stat of 205. Rockslide for flying types, X-Scissor for Psychic and Grass. Protect to let sandstorm slowly chip away at your opponent's health.
I'd type more but uh.. Super Bowl soon :P
p.s. Wrong forum ;)