From the 29th of January to the 11th of February, there will be a wi-fi event for the DS Pokemon games. (Pokemon Diamond, Pearl, Platinum, Heart Gold and Soul Silver) If you are able to connect your DS to Wi-Fi either at home, or in a public network, you'll be able to download this...
"10th Anniversary Mew Download
Games Obtainable With: Diamond, Pearl, Platinum, Heart Gold, Soul Silver
Available from: January 29th 2010 to February 11th
This event gives you a special Mew. This Mew doesn't give any special effects in the game. The details of it are as follows:
Date of Obtaining ???. Apparently had a fateful encounter at Lv. 5
View the details at Serebii.
Your one won't look like a retarded alien, sadly. =D That sprite is awesome hehe...
Totally looking forward to this, been looking for an excuse to turn my pokemon game back on. I'm so sad... =3
Also, if you like pokemon and stay in America (or somewhere else with Gamestop stores) check this out: Link
Edit: I was dissapointed to find out that this is only in North America at the moment. I wanted a Mew T_T