I have a level 80 Parasect with False Swipe and Spore with 30 dusk balls and I wasn't able to capture him the first time, it barely tilted... and it ran out of moves, too. It has worked like a charm for legendaries in Pokémon HeartGold... And I have tons of captured pokémon 431 to be exact.
I don't have the Masterball, I used it on the Tornadus since roaming pokémon are so annoying to capture.
He's the last legendary, I need in White I've caught all the rest. I also have all the legendaries from Diamond and HeartGold, too.
Currently playing: Animal Crossing: New Leaf (3DS), Final Fantasy VIII (PS), Dragon Quest VIII (PS2), Super Mario RPG (VC), Assassin's Creed 3 (Wii U)