Primarily beat the gym leaders and beat the elite four
johoto or kanto regions
Usually when you have half of the pokedex filled he calls you and says "wow you have Pokemon not blah blah to johoto or kanto regions D:<
You can't.
sadly no
You can't go to Johto in Pokemon FireRed or LeafGreen.
Blackthorn City in Johoto
you cant go to johto but you could catch johto Pokemon on sevvi islands
chikorita - grass. cyndaquil - fire. totodile - water.
only in re-runs.
You can get it by transferring the Johoto starters via your Game Boy Advance to Pokemon Emerald
There is no best Pokemon on Pokemon HeartGold.
go on serebii.net (just type in Pokemon pearl pokedex) click on the one that says johoto