Rayquaza will want Hasty most of the time to outspeed non Scarf Reshiram and Zekrom. Even with paralysis support, the opponent might not always be paralysed!
Jirachi needs a Careful nature to survive longer. That haxy paraflinch combo will more often than not fail to KO both Giratina or Lugia. Iron Head does little damage to them. Giratina can take his time to cripple you with Will-O-Wisp, Lugia can Reflect and both has Pressure which will probably out stall Jirachi. In fact, I think Rayquaza is the one scaring off Giratina not Jirachi beating Giratina.
Going to wait for the Uber moderators opinion before putting this combination up.
NOTE: Fireburn please help me put it in the OP if you like the combination. School sucks. Not much time to update it at the moment ;_;
<&GreatSage> if nothing else it's a "trickroom teaches pokemon" thread
<&GreatSage> which is reason enough to keep it
<@Colonel_M> I once heard Jibaku considered Scarf Gyarados for his Ubers team
<syrim> Trickroom the ultimate synguuest