I think between the hours of 8PM and 4AM in the morning only.
In short, when little children should be in bed asleep.
In the Ilex Forest at night.
yes
Get a life and stop playing Pokemon at 11:20 at night.
To get Gastly you have to go to sprout tower at night.
In the Kanto region go on route 7 (night only)
no you can trade soulsilver pokemon to black
he is not in Pokemon soulsilver or Pokemon heartgold
POKEMON SOULSILVER come with a poke walker and the Soulsilver game
Pokemon soulsilver and Pokemon heartgold are basically the same game just different versions but i do recommend buying Pokemon soulsilver
unlocks night skys edge on the pokewalker
SOulsilver
You can find Haunter in SoulSilver in Route 8 at night. Additionally you can catch a Gastly at night in the Sprout Tower or the Bell Tower and then you can train it until Level 25 which is when it'll evolve into a Haunter.