I'm not sure what would be better in the last slot - HP Rock, or Pyschic. How much does Pyschic do on Dnite and Gyarados after +2 SpAtk?
If it doesn't OHKO them, I'm going with HP Rock and hoping that I don't see many Kerudio :/
LO timid Urgamoth psychic does 66.2% - 77.9% to standard RestTalk Gyarados, very small chance to OHKO after stealth rock. Note that this is pretty much the bulkiest version of Gyara, all others are easily OHKOed after SR.
252/252 Dragonite takes 49% - 57.8%, a 2HKO. Note that this version of Dragonite (DD+Heal Bell) usually only runs Dragon Claw as their attacking move which doesn't OHKO back, so Uru still wins. Almost all other versions are OHKOed after SR.
Salamence is always OHKOed with SR (with good chance of OHKOing even without it).
Out of those 3 pokes, only Rest-talk Gyarados can actually defeat Uru. Stealth rock is crucial though, but as i said in some post earlier, Uru needs lots of support, and stealth rock isn't that difficult to set up.
Note however that if you go for HP rock, you have no chance whatsoever to defeat Kerudio and Terakion (although you do get neutral hit on heatran).
True, but after +1 Spe, very little will be able to outspeed and Twave it, unless they can survive a +1 STAB attack. Do you think Jirachi can survive a +1 Fire Dance and then Twave? Probably not. The only Twaver I can see surviving Uru's attack is Blissey. And there's probably more Twavers from Gen. V that might be able to do that.
Lum berry actually could be pretty useful, I think I'm gonna test Lum Berry first before I try LO. Great idea :D
I found Lum berry most useful when setting up. One of the best setup opportunities for Uru is Nattorei (who i saw on like every single team). Uru resists both it's STABs and also threatens KO back, however since Butterfly dance is so predictable, Nattorei might try to Twave instead of switching. Same goes for Jaroda who cannot do much with it's attacking moves (well, as long as it doesn't have +6 SpA :) ), but it can paralyze with glare while you use Butterfly dance.
Also, even after Uru is at +1 spe, there's still mischeavous heart pokes. Erfuun might try to stun spore as a last ditch attempt to stop the sweep, even if it will sacrifice itsef doing it (i stopped Urugamosu and Doryuzzu sweeps like that quite a few times) and lum would be of great help in that case.