New Pokémon WiFi Download Event: Enigma Stone. From July 31 to August 27 you can connect to Nintendo Wi-Fi through Pokémon HeartGold or SoulSilver to receive an Enigma Stone which can then be taken to to the fossil-reviver guy at the Pewter City Museum who’ll turn it into Soul Dew which boosts the Special Attack and Special Defense of Latios & Latias when held.  Shortly after, Latias will show up to battle you if you’re playing HeartGold, and Latios in SoulSilver.

[Via Serebii]