Ha, trachy lost in the first round and I won the whole thing.
We made our teams as foils to each other. He went Rain and I went Sun.

Groudon @ Ground Gem: Bringer of the sun and great Physical attacker. Ground Gem+Helping Hand gives Earthquake a very good chance of OHKOing Kyogre.
Trait: Drought: Needed as its ability. Helps out itself and Arceus.
EVs: 64 HP / 252 Atk / 192 Spd: trachy has his Mewtwo outspeeding Deoxys-S with Tailwind. I have my Groudon outspeeding Mewtwo with Tailwind. I think mine is more reasonable, as it allows me to go more bulk.
Adamant Nature (+Atk, -SAtk): More offense.
- Earthquake: STAB and hits all other Pokemon. My team is prepared for this, the other team not so much.
- Rock Slide: Hits those opponent's who won't be hit by Earthquake.
- Fire Punch: Gets that boost from Drought. It's used to hit those rare threats like Skarmory and Ferrothorn.
- Protect: Gives me a safe turn that my Pokemon can use to take down a threat.

Whimsicott (M) @ Mental Herb: My support Pokemon. Mental Herb allows me to recover from Taunt and Encore, which would cause me major problems.
Trait: Prankster: Allows me Tailwind and Encore to get priority.
EVs: 252 HP / 252 Def / 4 Spd: I have to stack on the bulk so Groudon's Earthquake doesn't kill me. It makes me more vulnerable to other Whimsicott, Tornadus, and Thunderous, but that is a risk I am willing to take.
Bold Nature (+Def, -Atk): Further boosts my defense.
- Tailwind: Makes my Pokemon faster.
- Giga Drain: In case I do get Taunted. It also helps in taking down threats such as Gastrodon, Swampert, Quagsire, Kabutops, and Omastar. And does decent damage to any other Ground or Water type foe.
- Encore: I can trap my foe in a Protect or Trick Room, as well as any other stat move. This brings my opponent down to one Pokemon.
- Helping Hand: Boosts Groudon's (or any other Pokemon's) power.

Arceus (Arceus-Fire) @ Flame Plate: Sure Fire might be weak to Surf, Water Spout, Rock Slide, and Earthquake, but it gets the STAB boost for Fire type attacks. Flame Plate makes it a Fire type and further boosts the power of Heat Wave.
Trait: Multitype: Needed ability.
EVs: 252 SAtk / 4 SDef / 252 Spd: Makes Arceus fast and powerful. Can outspeed a number of foes even when Tailwind is not in effect.
Modest Nature (+SAtk, -Atk): Boosts my Special Attack. Speed is not as much needed due to Tailwind.
- Heat Wave: STAB+Drought+Flame Plate off of 100 base power and hitting both foes KOd a lot of my enemy in the tournament.
- Ice Beam: Coverage against Dragon types.
- SolarBeam: Coverage against Water, Rock, and Ground types. It doesn't have to charge with Drought.
- Protect: As I have Earthquake on Groudon, I need this to dodge. Plus it allows the rest of my team have the time to take down threats to Arceus.

Zekrom @ Dragon Gem: Helps out against Dragons and Rain teams who threaten this team. Dragon Gem is to make up for Dragon Claw's base power.
Trait: Teravolt: Needed ability.
EVs: 4 HP / 252 Atk / 252 Spd: Max Attack and Speed. Speed is higher because I don't care as much about bulk for this guy and it helps it function outside of Tailwind.
Adamant Nature (+Atk, -SAtk): More power.
- Bolt Strike: STAB. Hits Water types incredibly hard.
- Dragon Claw: STAB. Hits Dragon types hard, especially with Dragon Gem.
- Protect: Same as with Arceus.
- Rock Slide: Hits multiple foes. This is for when my opponent has two very weak Pokemon out and Rock Slide could finish them both off.