Standard mixed set seems to be 40 Atk/252 SAtk/218 Spd with either Naieve/Rash Nature and
-Draco Meteor
-Fire Blast/Overheat
-Extremespeed
-Brick Break/Outrage
Rayquaza vs Top 10 Most Used Pokemon in Wifi (December 11, 2010 stats)
1.
Nattorei;
Rayquaza outspeeds and OHKOs Nattorei with Fire Blast.
2.
Tyranitar;
Brick Break is a clean OHKO. If Brick Break is not being run, the next most powerful move is Draco Meteor which is a 90% chance to OHKO without hazards.
Rayquaza@Life Orb (40 EVs, Neutral Nature) Brick Break vs Tyranitar@Choice Scarf (0/0 EVs, Neutral Nature): 112.6 ~ 132.5% (384 ~ 452 HP)
Rayquaza@Life Orb (252 EVs, Neutral Nature) Draco Meteor vs Tyranitar@Choice Scarf (0/0 EVs, Neutral Nature): 97 ~ 114.3% (331 ~ 390 HP)
3.
Scizor;
Any fire type move OHKOs. Scizor's Bullet Punch only gets a 1% chance to OHKO.
Rayquaza@Life Orb (252 EVs, Neutral Nature) Fire Blast vs Scizor@Life Orb (0/0 EVs, Neutral Nature): 324.5 ~ 382.9% (912 ~ 1076 HP)
Scizor@Life Orb (252 EVs, +Nature) Bullet Punch vs Rayquaza@Life Orb (0/0 EVs, Neutral Nature): 43.5 ~ 51.2% (153 ~ 180 HP)
4.
Doryuuzu;
Outspeed after Air Lock and Fire Blast OHKOs.
Rayquaza@Life Orb (252 EVs, Neutral Nature) Fire Blast vs Doryuuzu@Balloon (0/0 EVs, Neutral Nature): 149 ~ 175.6% (538 ~ 634 HP) (Sandstorm)
5.
Gengar;
Draco Meteor OHKOs, Outrage OHKOs, Fire Blast is a 42% chance, Overheat is a 90% chance...I'm not even going to copypaste the stats we all know Gengar is frail as hell.
6.
Garchomp;
Garchomp outspeeds and OHKOs with Outrage, and Dragon Claw if stones are up. Stone Edge is a 36% chance with stones up. Rayquaza cannot 2HKO with Extremespeed.
Garchomp@Choice Scarf (252 EVs, Neutral Nature) Outrage vs Rayquaza@Life Orb (0/0 EVs, Neutral Nature): 121.9 ~ 144.1% (428 ~ 506 HP)
Garchomp@Choice Scarf (252 EVs, Neutral Nature) Dragon Claw vs Rayquaza@Life Orb (0/0 EVs, Neutral Nature): 82 ~ 96.2% (288 ~ 338 HP)
Rayquaza@Life Orb (40 EVs, Neutral Nature) Extremespeed vs Garchomp@Choice Scarf (0/0 EVs, Neutral Nature): 31.9 ~ 37.8% (114 ~ 135 HP)
7.
Roobushin; (Most used set is Adamant/Brave - EVs: 120 HP / 252 Atk / 136 SDef)
Rayquaza outspeeds and OHKOs with Draco Meteor. Nothing else OHKOs though, and -2 Draco Meteor doesn't OHKO. Roobushin OHKOs back with Guts boosted Stone Edge, also a OHKO without Guts boost if rocks are up.
Rayquaza@Life Orb (252 EVs, Neutral Nature) Draco Meteor vs Roobushin (120/136 EVs, Neutral Nature): 102.3 ~ 120.4% (390 ~ 459 HP)
Roobushin (252 EVs, +Nature) Stone Edge vs Rayquaza@Life Orb (0/0 EVs, Neutral Nature): 78.6 ~ 92.8% (276 ~ 326 HP)
8.
Heatran
Brick Break doesn't OHKO. Returning Dragon Pulse doesn't OHKO. Rayquaza wins this.
Heatran (252 EVs, +Nature) Dragon Pulse vs Rayquaza@Life Orb (0/0 EVs, Neutral Nature): 67.2 ~ 79.2% (236 ~ 278 HP)
Rayquaza@Life Orb (40 EVs, Neutral Nature) Brick Break vs Heatran (0/0 EVs, Neutral Nature): 60 ~ 71.2% (194 ~ 230 HP)
9.
Burungeru;
Nothing Rayquaza has can OHKO Burungeru. Burungeru's returning Ice Beam can OHKO if Rocks are up.
Burungeru (4 EVs, Neutral Nature) Ice Beam vs Rayquaza@Life Orb (0/0 EVs, Neutral Nature): 75.2 ~ 88.8% (264 ~ 312 HP)
Rayquaza@Life Orb (40 EVs, Neutral Nature) Outrage vs Burungeru (252/0 EVs, Neutral Nature): 81.9 ~ 96.5% (331 ~ 390 HP)
10.
Politoed
Same situation as before. Rayquaza cannot OHKO Toed, and Toed OHKOs after rocks.
Rayquaza@Life Orb (40 EVs, Neutral Nature) Outrage vs Politoed (252/0 EVs, Neutral Nature): 81.2 ~ 95.5% (312 ~ 367 HP)
Politoed (4 EVs, Neutral Nature) Ice Beam vs Rayquaza@Life Orb (0/0 EVs, Neutral Nature): 78.6 ~ 93.4% (276 ~ 328 HP)
That's 6/10 Rayquaza can kill. Three of those that he can't OHKO rely on rocks and are pretty wrecked after Rayquaza is done.