Missingno is not an available glitch in Pokemon SoulSilver. Missingno was a glitch that has long since been removed from the game (unless you use an AR to hack the game).
it is hidden in route 20 near the entrance to seafoam islands
Use the Dowsing Machine on Route 20. You'll eventually find one.
You can't. You have to evolve it from Ralts at level 20. You can find these in route 34, however, you only have a 20% chance of finding them. Good luck! Hope I helped!
20
level 20
You can only get the Birds after obtaining all 16 badges Articuno: at the Seafoam Islands on Route 20 all the way down on BF4. Zapdos: on Route 10 right near the Power Plant. Moltres: in Mt. Silver
on soul silver, heart gold you can get it on route 47, you get there by going through the gate in cianwood city, there on route 47 you can get it by surfing on lever 10-20 and also that route follows to safari zone, in sinnoh you can only get in on Pokemon diamond on route 226 and 230 but it's uncommon, in kanto you can get it at seafoam islands
In HG/SS you can find one in route 20, using the dowsing machine. It can also be attached to Relicanth and Lanturn. In D/P/P I do not know
After 20 days, if you clodder the Marshland Area with Forest items, a Level 44 Croagunk will appear. But there is an easier way, catch one on Route 212 in Platinum.
20
Rattata evolves into Raticate at level 20.
Hoothoot evolves at level 20 in to Nocowl.