1st of all it is Raikou and by roaming Johto
you have to use faulse swipe and when you see it again use an ultra ball
you have to fight your way to the bottom of the tower. there, you will find suicune, raiku, and entei. then, when they see you, they will run away and you have to catch them(either catch or defeat, really).
you dont
catch it in the wild
It's not A Raikou, its Raikou, as you only get one/two chances of battling him/her and it's legendary I would recomend getting it down to barley any life left and asleep. Catch with a fast ball
It's your opinion, but in HeartGold you can catch Ho-oh, Suicune, Raiku, and Entei, and in SoulSilver you can catch Lugia, Zapdos, Moltres, and Articuno. There are also more Pokemon available in HeartGold than SoulSilver. Edit: The person who last answered this question is wrong, you can catch all of the above Pokemon in both games, not in either or. I know this because I have soul silver and I have suicune, raiku, Entei, Ho-oh, Lugia, Zapdos, Moltres, and Articuno; so obviously you must be able to catch them in both.
You can't.
You can't catch Rotom in heartgold.
you catch raikou on the last gym leader in the kanto leaders and you catch uxie in vermillion city from
ia Ho-Oh Lugia Entie Suicone Raiku and the red gyrados
look around for Suicune/Entei/Raiku
You can catch Mewtwo, Suicune, Entei, Raiku, Ho-Oh, and Lugia.