right now (december 22) there is an event at GameStop where you can get one of the legendary 3 dogs shiny
the only way you can do it is to win the next event or use cheatcodes
I doubt there will be another one. HeartGold and SoulSilver are part of the generation IV pokemon games, and right now the most recent gen is generation V
Celebi
There isn't a date for the Arceus Event in Pokemon HeartGold (unless you mean the event where you get Arceus). When you send over any Arceus into your HeartGold game, the event is activated. You'll have to go to the Ruins of Alph in order to do the event.
An event
Through an event.
Yep
You can't.
there is a Nintendo event maybe at gamestop and go to it with Pokemon heartgold and soulsilver and there you will get celibi
To get a Mew in Pokemon Heartgold, you could do it through a Nintendo Wi-Fi event.
some time after Pokemon black and white comes out in spring 2011 march 6
you can get celibi on heartgold only from a wi-fi event