If you can collect all the 26 letter forms of Unown form including the Exclamation and Question mark. You can fused them all using "secret key item" to become the Ultimate forme of Unown. What so good about this is you can randomly produce a Pokemon (from Bulbasaur to Z). Yeah that's right guys, ransom Pokemon. Here's your chance to have that legendary pokemon you always wanted.
You would have a 28/XXX chance of getting another Unown for all the effort. So yeah...I think I'll pass.
You can only do this once per game. Get ready to soft-reset about hundreds of time. If you aren't lucky enough.