The Enigma Stone is very similar to the Eon Ticket. Like the Generation III event item, the Stone will trigger the appearance of the Eon Pokémon not found roaming in the version being played. In HeartGold, this is Latios; in SoulSilver, this is Latias. Also much like the Eon Ticket, the player must have defeated the Elite Four and received the National Pokédex before the event can be triggered. The Enigma Stone may be downloaded by anyone who has received the Pokédex, but they must first complete the requirements mentioned above before they can trigger the event.
If it is taken to the Pewter Museum of Science, traveling Pokémon Champion Steven Stone will have a researcher examine it, who discovers that it is really the Soul Dew. After this brief encounter, depending on the game version, one of the twin Eon Pokémon will attack the player, presenting the opportunity for it to be captured. It will keep returning to the same spot until captured.
This item was available via Wi-Fi to the Japanese versions of the games from November 27, 2009 to January 11, 2010 and the North American and PAL versions from July 31, 2010 to August 27, 2010. In Japan it was revealed along with the event for HeartGold and SoulSilver, the 10th Anniversary Mew.