Cloyster can defeat Garchomp with no problems,as Garchomp may outspeed it when unboosted,but Cloyster has enough natural bulk to survive any physical attack Garchomp can throw at it before setting up a Shell Break (which makes Cloyster more than viable) and taking it down with Icicle Spear.
Look at the date of my post please. October 3rd. We didn't know what everything did back then. We didn't know the absurbity of Shell Break Cloyster.
Who, by the way, really dislikes eating a Stone Edge from Garchomp, especially if Garchomp is at +2, and especially is SR is up.
Basically:
Garchomp comes in!
*Switch to Cloyster*
*Swords Dance*
Garchomp used Stone Edge/Outrage!
Cloyster Fainted!
Either that, or Cloyster comes in to revenge kill. In which case, you can just LOL and send in Scarfgon, and Stone Edge it. [Who outspeeds +2 Cloyster. Cloyster is not fast in the first place.] Or, even better, just scare out Closter with... say, Roopushin. Assumeing rocks are up, Closyer can only play that game so long.
This seems like it could work, but...
Oops, that's right, Sazandora is a Dragon with Levitate and U-Turn too. :0 Between Garchomp and Sazandora (and even Landlos, who has a stronger Earthquake, U-Turn, and higher Speed, even if it doesn't have that secondary Dragon type), Flygon is gonna have a pretty hard time fitting into 5th Gen's OU. :0
Sazandora is slower, Flygon is a better check to other Sazandora. He also has a better typing. Sazandora is weak to Dragon, Ice, Fighting and Bug. Flygon is only weak to Ice and Dragon. He also dosen't fear random Thunder Waves.
Landos lacks the Dragon type, which is very important, really, as Flygon was excellent at cleaning with Scarf Outrage after the removal of Steels. Sure, the new dragons do that better, but that's something Landos dosen't have.
Yes, Flygon will find it hard, but he still has his niches, and is still an excellent partner to Garchomp. It's like using Salamance and Dragonite on the same team late Gen 5, to muscle past their counters. Very few could handle both.