Weaken him to red hp use thunder wave on him then use many ultra balls eventually you will get him.
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you can, the catch is fairly easy even without a masterball although I woul use ultra balls if you arent going to use a masterball. I you knock out reshiram without sAVing before hand you can try again after the credits at dragonspiral tower
Use a masterball,parilize it,constently huck balls at it,damage it.
it easy get it down to 10 hp and use a net ball easy i done it
MasterBall
the legendary Pokemon are different levels when you catch them. also in crystal there is a battle tower where when you beat it you can catch suicune without a masterball because you can battle him without him running away.