you have a black card
No.
there a Pokemon that are shaped like all the leters of the alphabet and the signs ! and ? they feature in Pokemon movie 3 : spell of the unown
Unown is a Psychic type pokemon.
There is no powerful Pokemon. All the Pokemon found in the ruins are Unown. The special ones you may be thinking of are the new "?" and "!" Unown.
in the tanoby ruins
After collecting all 26 Unown, talk to the scientist and he will let you print out your Unown shapes.
The tunnel on top the ruins is accessible.The tunnel is where you catch the ? and ! Unown.
sure are
All of them
You have to get all the Unown, A-Z, so that guy will complete the tunnel. There you will find Unown ? and !. If this is not what you are looking for, please rephrase the question.
As rare as any other shiny pokemon: a 1 in 8192 chance
they spell the alphabet and maybe you get a rare Pokemon