any day
Go to the Pokemon Centre in Eterna City and speak to the brown haired girl, she will hand you the Pokétch app "Friendship Checker".
They don't, he is your rival throughout the whole game and if he wasn't present you would not have a rival.
In Nimbasa City to the top left of the Pokemon Center there is a house with a blue haired kid in it. Talk to him for Strength.
you have to use hm rock smash on rocks to find them.
On wild Pokemon and serval locations.
It attracts a ledendary pokemon.
he is in a cave across from cerulean city (Kanto), a green haired ace trainer is guarding it
You find out when you get the Celebi from the Pokemon event in February.
You can find them in the Underground
underground
you can find information on Pokemon heart gold and soul silver on this website www.bowserrules.piczo.com
pokemon heart gold