Its easier to catch it with about 30 dusk balls, I cought Zapdos, Moltres, Suicune, Mewtwo, and Lugia with dusk balls. Get its HP in red then throw dusk balls, each 5 dusk balls throw 2 ultra balls, then back to dusk.
I caught it when I put my espeon into battle so when it froze me it froze itself due to sincronize then I just through ultra balls.
You have to get all 16 badges and then go to seafoam islands.
Ive caught entie suicune riakou moltres zapdos articuno ho oh lugia and mewtwo so if you need any help with any of those just ask me, for aticuno you get all 16 badges then go to the seafoam islands, I sugest you have a pokemon with a status problom effect like paralize or sllep or freeze (its hard to freeze considering its ice type) but any other status effects could defeat it then weeken it as muck as you can, bring as many ultraballs and great balls as you can (because it took me more than 19 ultra balls and 7 great balls) then throw ultra balls and great balls at it until you catch it.
For help look at a walkthrough as it is slightly tricky to find!!!
You don't have to have all kanto badges I caught him with 6 badges
I got it as low as its health goes without it fainting, used almost every pokeball I had. & whats it do? Uses struggle & hits itself w/recoil. T~T so I restarted my ds just to find I hadnt saved since like, pallet town. Depression.
How you catch it is you go to seaform island in kanto but bring about a 100 ultra balls because it is at lv. 50
You go to seafoam islands and get through this puzzl he's at lvl 50 and VARY hard to chach
Just spam ultra balls