In HeartGold I mean. I got all 28 in Platinum and don't remember getting anything.
Well, in pokemon pearl or daimond you go to the little boy near the ruins and show him an Unkown then he will give you a Alphabet seal depending on the unkown i find them usefull in wifi to spell my name or somthing I like.
In Heartgold/Soulsilver, there is little clarity about what does happen, but you must go to the arceologist station to get the item/s
You also gain acess to hidden cave on the route south of veilstone city. there used to be a guy there in front of a wall but when you go back with all the unknown there will be a path and a rare candy awaits you
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