you need tu use markingmap so you can find it!
by searching in the grass
giratina,mespirit,uxie,azelf,darkai,shaymin,cressellia
I think it should be Mespirit because Mespirit may have all around stats but these are really low and it doesn't learn any good attacks.
Uxie, Mespirit, and Azelf are unavailable in Pokemon SoulSilver. They can, however, be traded from a Diamond, Pearl, or Platinum game, or transferred from a Gen III game.
you can only get one mespirit in Pokemon diamond, pearl and platinum; unless u cheat.
it allows you to find roaming Pokemon such as cresselia and mespirit
i don't think anything happens.....
TheSinnoh Dex Legionaries are:(Rotom),Uxie,Mespirit,Azelf,Dialgia,Palkia,(Heatran),(Regigigas),(Giratina),(Cresselia),(Phonie),(Manaphy),(Darkrai),(Shaymin),and (Arceus) (Names in ( ) are National Dex in D/P and in the Sinnoh Dex in Pokemon Platinum)
they are awesome LEGENDARY pokemon....if u dont think so u dont need to catch them
well, you can get glameow wearas in dimond there is stunky. also, you can get palkia, shaymin, zapdos, moltres, articuno, cressilya, azelf,mespirit,uxie and heatran (some of the legendries you can find in diamond and platinum.) hope this helps!
In The Middle Of The Lake Like All The Lakes.
buy the Pokemon platinum book