4× if used on the first turn of a battle in DPPtHGSS
I caught Dialga in an Ultra Ball on the first try with full hp.
I had a surprisingly easy time catching all the legendaries in Black and White, especially after the hell that was chasing the dogs and Latias in SS. It took me weeks to catch all four of them, and I vowed to master ball every possible potential roamer after that. It's made life infinitely more pleasant.
I think I caught Zekrom in one or two ultra balls - after dealing with SS, I was stunned at how easily a legendary would oblige my request for ownership.
tomorrow's just a song away.