You are talking like 9800 is a hard to get in BW o.O
9800 is nothing in those games.
I'm not denying that. Like I said, the item guy at Nurse Joy's counter at Icirrus' Pokémon Centre will give you that for one Star Piece (you need two at a Pokémart, those scam artists). By the time you "step" to Lv.98, you'll probably have five or six of those if you go seeking them.
Meanwhile, I just reread about Heart Pieces being obtainable at Driftveil this morning. I need to start looking at those options and stock some away in case I need a Pokémon to relearn a move for breeding. I do intend to become both Pokémon Master and breeding superstar. ;) Shinies not so much, but I will accept them in trades; is there a difference when breeding with Shinies? ;)
Depending on which version you have, you probably want to use it {Master Ball} on the roaming legendary, as it tends to give the most grief to people. You also get two in the game, so you could use the other on Kyurem or Landorus or save them in case you ever find a shiny exploding Pokémon. Don't use it on Reshiram/Zekrom as they have the same catch rate as an Onix.
My roamer strategy was different. The evening I unlocked it by getting the Legend Badge and heading to Route 10 (where I'd been multiple times, but the event only occurs then), I didn't have a lot of time up to midnite, so I went and started wittling away its HP in two or three encounters. I then hit the end of the day; in the early morning it started hanging out in the eastern Unova areas out of my reach (at that time). That bugged me, but I did my other daily business at that point and spent the overnite at Nimbasa Town. While in bed, I decided to bring my Watchog (Super Fang and Hypnosis FTW!!!) to the fight. Since it knows Mean Look, all I had to do was flash the look on my free first turn and that roamer was done roaming. The next morning, I executed my plan on Route 5. I failed once as Watchog got dropped, then Tornadus ran away next turn. My second attempt went in my favour and I captured it, I think in a Dusk Ball or Great Ball or something. So my Master Ball sits unused. I'm stupid like that, I do things the hard way.
As for getting two in game, there is indeed a second, but I think you have to trade so many times and then get it at a Pokémon Center (Castelia?) as a reward. There are other items too.
You can easily spread Pokerus by placing the infected pokemon first in your party and battling a wild pokemon with it. There is a large chance to pass it to the second and third pokemon slots.
It doesn't have to be the first slot. In fact, if the other five are unaffected, placing it in the middle spreads the "disease" quicker. I would plant them at the second and fifth slots, and 2-3 battles later, back to the PC to redeposit.
I haven't infected my newest recruits yet, but my Musketeers (who I was going to keep pure) accidentally joined some Pokérus holders, so they are now doubling their EVs. Not like it matters. I don't think they can go on Wifi.
Cyclone