go to psypoke.com and go in psylab, it tells you
Mew
All Letters and theres now a Question Mark and a Explanation Mark......
Unknown(sorry about my spelling) Letter A is the rarest Unknown in all games. You are more likely to find a shiny Pokemon then Unknown A but if you are dedicated then go for it but prepare for...
The Solaceon Ruins.
Red and Blue, I think. Maybe Yellow but I'm not sure.
they can be used to acces a new area if you collect a-z.This new area has the 2 other unowns and the hippomatas.
Pokemon HeartGold and SoulSliver Nintendo Summit 10 Trailer
Pokémon Diamond / Pearl Walkthrough Part 31
Pokemon Black and White Video Review
Pokemon Black and White Version: Battle Trailer