What are rare Pokemon in HeartGold?

Answer 1

Some of the rarer Pokemon include the three starters (Chikorita, Cyndaquil, and Totodile) as you may only get one at the start of the game. Trade with your friends or on Wi-Fi to get the other two.

Some other rare Pokemon and Legendaries:

Pineco---Use the Headbutt attack on trees

Wobbuffet---Found in Dark Cave or the Safari Zone

Tyrogue---Explore the depths of Mt. Mortar to find the Karate King. Defeat him to get Tyrogue

Magby, Smoochum and Elekid---Breed Magmar, Jynx and Electabuzz with a Ditto, respectively

Natu---Surf in Union Cave until you find another exit. You will Find yourself outside the Ruins of Alph. Walk in the grass outside to find a Natu

Eevee---Get it from Bill in Kanto

Porygon---Trade in a large amount of tokens for this cyber Pokemon

Legendaries:

Articuno---Seafoam Islands

Zapdos---Power Plant

Moltres---Mt. Silver

Raikou and Entei---Roam Johto after your Ecruteak encounter

Suicune---Route 25

Ho-oh---Bell Tower

Lugia---Whirl Islands (After you get the Silver Wing)

Mewtwo---Cerulean Cave