This is the first competition where I now have more wins than losses, and I am a first-hand witness of how horrifying a Darmanitan-Mamoswine (both 31 Speed and Attack IV Jolly) combo can become. Even I did not expect the Mamoswine to outspeed anything (I gave it a Liechi Berry so that it can revenge after tanking a hit), but it managed to surprise me (and the opponent) everytime by outspeeding almost everything, even a Haxorus. Then again, getting both to have those IVs took much cycling up and down Route 3 and abandoning unacceptable Pokemon, Nazi-style (I have a lot of DWF Swinub from my last breeding program).
The only one match I lost was when for some reason, my Darmanitan's Rock Slide (90% accurate) did not connect after the opponent's Thunderus-I (Nasty Plot set, not the Prankster set I was expecting) managed to KO my Mamoswine with a 70% accurate Focus Blast. The most frustrating part had to be that my Darmanitan was actually faster than the Thunderus, and that the Rock Miss cost me my team's momentum and thus the match.
2 Rage Quits today. Battle progress of the two offending matches are as follows:
VS. JOSE, from Andalusia, Spain. Rating: 1389
Active Pokemon: Starmie, Accelgor, Terrakion
Reserve Pokemon: Toxiocroak, Weavile, Electivire
Turns out Starmie are very fragile and can be outsped by an absolutely-maxed out Darmanitan. (I KO-ed the lead Starmie with a U-Turn that I did not expect to turn into a 1HKO. It was not a critical even) I continued the match by setting Spikes under Accelgor using my suicide Ferrothorn, which was actually able to tank Accelgor, so I switched to offensive mode and Gyro-Balled Accelgor to dust. The Terrakion after that got spiked and then dusted by another Gyro Ball.
Final score: 3-0 Clean Sweep
He rage-quitted after the end of the game, but it was too late: Nintendo's servers have already recorded my win over him.
VS. JOSH. Rating: 1434
Active Pokemon: Seismitoad, Chandelure, Archeops
Reserve Pokemon: Conkeldurr, Cobalion, Mienshao
I had an 'oh sh!t' moment when he brought out his Seismitoad and I brought out my Darmanitan, but I managed to pick up the pace by U-Turning out (seriously, this is my favorite move: It got me out of sticky situations like a charm) to my Ferrothorn. There I started to annoy him by using Leech Seed and Spikes, as the Ferrothorn laughed at the Seismitoad's attempt to KO it with Drain Punch (It lost more than it recovered except for the time it managed to get a crit). I put the Seismitoad out of its misery using Power Whip after Ferrothorn had its fun. Ferrothorn later got roasted by Chandelure, but was quickly avenged by a Sheer Force-Life Orb-boosted Rock Slide from Darmanitan (it missed once though, causing it to get Toxic-ed). Darmanitan later got destroyed by Archeops after missing another Rock Miss, but again, it was avenged by Mamoswine's Icicle Crash.
Final score: 1-0 Revenge Pileup success
He rage-quitted in time for Nintendo to not record the win.
I checked the stat calculator. Turns out my Mamoswine has a speed of 89 at level 30 and my Darmanitan has a speed of 99 at level 30, which means they can outspeed a ridiculous number of opponents. The fact that weather-based teams are way less common in this tournament probably helped my case, though I still pack a Sand Rush Excadrill (Jolly, also max Attack & Speed IV & EV) to counter Tyranitar and its friends.