nothing you just have them
nothing
you can read the unknown and you unlock ? and ! unknown
catch all the unknowns
they give you a legendary
In the games that came before heartgold and soulsilver, I don't believe anything special happens. In Heartgold and Soulsilver, you can now catch the last 2 unown (the "!" and the "?") in the Hall Of The Ruins Of Alph. Then the scientist that gave you the unown recorder comes out and gives you a pat on the back...
You catch unknowns.
Nothing is known about what happens after achieving capture of all 26 Unknowns. Sorry to disappoint.
you battle celibe level 5
yes in the Solaceon Ruins
in the ruins of alpha after you solve the puzzles
read the wall and catch all the unknowns
Once you catch all of the Uknown, you can go to the town with the day care and go to one of the houses and trade them in for letter seals. other than that they don't unlock anything.