You can easily run Serperior in OU.
The only thing you have to worry is about is Heatran and Dragonite.
Substitute / Leaf Storm / Hidden Power Rock / Synthesis -Leftovers
+2 252 SpA Serperior Hidden Power Rock vs. 0 HP / 0 SpD Talonflame: 496-584 (167 - 196.6%) -- guaranteed OHKO
252 SpA Serperior Hidden Power Rock vs. 0 HP / 0 SpD Talonflame: 248-296 (83.5 - 99.6%) -- guaranteed OHKO after Stealth Rock.
Place serperior against a Hydro Pump from Rotom Wash, Sub while he switches to Talonflame, cripple him with Hp Rock.
It shits on Keldeo, Mamosiwhine, Rotom Wash, Slowbro, Sableye and it's Mega, Chansey, Terrakion, Choice Scarf Tyranitar, Excadrill, Azulmarill, Mega Gardevoir, Mega Gallade,Gliscor, Mew, Sylveon. Able to run Coverage Hp Rock to damage Talonflame and Charizard Y and possible Crobats.
Coverage Hp Fire to kill Scizor, Skarmory and Ferrothorn can be one-shot at 3x,
Dragon Pulse can be used to damage Lati@s, Kyurem-B.
It fucks half of OU mons, the other half at least 1/4 of them can be taken out with coverage moves.
This thing will climb to OU, just like did Mega Gallade and Mega Lopunny.