OK, here goes.
Heat 1-Kyurem-W vs Dialga
And straight off the bat we have 2 of the favourites, 2 hugely strong dragons. In secondary typing, they represent the dragon type's greatest offensive and defensive enemies in ice and steel. However, Kyurem's ice and dragon type attacks are balanced by the steel type's resistance to both. It can use a few very very powerful fire type attacks, but these only do neutral damage due to the dragon type. This is what makes Dialga so deadly, resistances everywhere. Dialga's STABs, however, both hit White Kyurem for super-effective damage. Both are specially-offensive nightmares, with huge special attack, but both have pretty limited special defense, meaning it really comes down to who hits the fastest, because neither can take the other's hit (Dialga's Roar of time, Kyurem's Draco Meteor.) And the faster pokemon is....Kyurem-W.
AND THE CROWD GOES WILD! THE DRAGON TYPE REPRESENTATIVE IS OUT ROUND 1 AND AT THE OTHER SIDE OF THE DRAW RAYQUAZA IS STARTING TO GET SCARED.
Heat 2-Terrakion vs Regigigas
I'm not even gonna. Regigigas is really only in here because it's the only normal-type legendary. Meanwhile, representing the rock type, Terrakion is a pretty good pokemon all things considered. Even without being overall better than Regigigas, Terrkion counters it beautifully. Its rock type combined with Regigigas'
teeny tiny movepool means it's pretty likely to resist every attack of Regigigas, especially because Regigigas is running confusion, paralysis and substitute, giving Terrakion a 37.5% chance of a hit. But when it does hit, which it's more than likely to do in the 5 turns Regigigas is essentially useless, it's with a scarily powerful STAB and super-effective Sacred Sword. Bye-bye Regigigas. And the winner is..Terrakion
Heat 3- Volcarona vs Groudon
Volcarona really didn't want to face a ground type in round 1. Then again, it also didn't want to face a water, flying or rock type, or another fire type that resists its STABs. But this is Groudon's to lose, because Volcarona can be one of the deadliest pokemon in the game....in sun. Groudon, you done screwed yourself. In sun, Volcarona outspeeds Groudon to deliver an STAB sun-boosted Flare Blitz (my choice for a reliable fire-type hit, which Volcarona needs, while having huge power. The recoil is irrelevant. If that's not an OHKO you're in trouble/defensively in no danger most of the time.) coming from 120 base power, with Volcarona's 135 base attack, and with the sun up, and the fact that Groudon doesn't actually resist the fire type, and Volcarona takes it in another OHKO. Good boy, Volcarona. :)
Heat 4- Palkia vs Keldeo
This is a water head-to-head with the honour of representing water in the quarter finals at stake. It's also a battle between one of, in my opinion, the ugliest pokemon and one of the best-looking. And yet ugly old Palkia is definitely the favourite. They will both be using their non-water type STAB attacks, Palkia's Spacial Rend and Keldeo's Secret Sword. Keldeo hits first, and hits hard with a 129 special attack 85 base power STAB Secret Sword. This hits Palkia's mediocre defense stat and deals it a lot of damage, but Palkia survives and responds with 150 special attack, 100 base power STAB, into Keldeo's subpar special defence. This is a one-hit KO, and gives Palkia the win in the match. Nice job, Penis