that Pokemon would be unknown!there are 26 variation of unknown they all are based on the alphabet and you can capture them at the solaceon ruins.also if you capture the unknown you can get letter seals and place them on your Pokemon!when you choose that Pokemon the letters will be there!
in Pokemon diamond pearl and platinum you evolve surskit at level 22 but in platinum you surf on route 229 ( desert route) 5% chance of finding it in the hoenn reigion route 114 as a suskit in diamond and pearl it is lvl 2 or 3 at lake verity as a swarm Pokemon
114 is Unown. This is how u catch it: Go to Solaceon town. Go to the right and jump over the last three ledges. The cave u come to is the unown cave. CATCH ONE! No other trainers have Unown and they only appear in that cave.