Yes you can. By taking a male or female Pokemon in the same egg group or using a Pokemon called ditto(can be used for any Pokemon)and put them in the day care. For example you can put a female Swellow and a male chatot and you will get a baby tailow. The female Pokemon makes the egg and the male teaches the baby some of his moves.
No, you cannot sell eggs in Pokemon HeartGold.
yes you can...you make eggs in all Pokemon games
evey Pokemon has an egg except legendarys and ditto
Yes, there is a special option in the union room
Daycare center located in Goldenrod city (south)
yes, depending on the Pokemon hatched from the eggs gender determines what Pokemon you get tho
There is no best Pokemon on Pokemon HeartGold.
there is no Pokemon Mansion in Heartgold.
you can go to Pokemon daycare with a male and female Pokemon and they will lay eggs of the same type of Pokemon but ditto can be either male or female it does not have one certain gender.
Of course you can!! It's just like in all the other Pokemon games.
They are not in Pokemon HeartGold
where is the pokemon transfer lab in heartgold