User blog comment:Zt-freak/3DS friendcode/@comment-1455034-20120709130454/@comment-1455034-20120709213225

If it isn't in your Pokedex, it is possible that someone Action Replayed your Pokemon White/Black game to give you unknown and prevent it from getting in your Pokedex. Another possibility is that you (somehow) don't have the National Pokedex yet. And why would you stop playing Pokemon just because you get three mysterious Unown spelling "Die"?