well i hate my game so live with it
this is an answer site not a site for critics okayMt.Moon
Mew can't be catched in Pokemon heartgold, only mewtwo.
Certai pokemons that come from events are not needed to complete the pokedex. Such as: Arceus Mew Deoxis Manaphy etc...
If you somehow manage to get it on HeartGold, SoulSilver, Diamond, Pearl, or Platinum, you can trade it to Black
u cant. its event exclusive-sorry. but go to cerclean cave, and eventually u will find a mewtwo. just as good right? not as cute as mew, though... :(mew2 is some where in cerulean cave