First beat EVERY Gym Leader in Kanto. Then, go to the Cerulean Cave. Now go to the end where Mewtwo is. I have no idea what level it's at but I have a feeling that the level is either 60, 70, or 80.
only after you've received the national pokedex and have got a poochyena.
get every Pokemon in the game then go to mystery cave and catch it
You have to trade from diamond,pearl or platium :) thats what it says in the guide book.
You can't catch Rotom in heartgold.
you cant catch him in heartgold you can only get him in soulsilver
You can never get Mew without hacking or getting it from a hacking friend. Besides, its Mew and Mew2 O_O
In HeartGold you can catch Kyogre.
You can only catch Vulpix in SoulSilver, not in HeartGold. You can catch it on route 36 and route 37.
No
In pokemon Heartgold
you cant catch it it is rare
yes you can catch every Pokemon ever made