First of all, you don't catch him, you receive him.
Once you have all 16 badges, go to the summit of MT.Silver, & beat trainer red, he has Pokemon from level 80 - 88, so bring your strongest Pokemon, once you defeat red, fly to Saffron city, go to the Silph Co. Go to the counter, & you should see steven, (some guy w/ blue-green hair) Make sure you have room in you team for another Pokemon, because he will tell you to pick a shard.
If you pick the green shard, then you get treeko, but if u pic the blue shard, then you get mudkip, red shard, tochic.
No.
You can't catch bastiodon in Pokemon soulsilver.
catch it? no.
Treecko cannot be found or caught in Pokémon Black.
No Sinnoh Pokemon can be found in HeartGold or SoulSilver, but you can choose just one of the Hoenn Pokemon after doing certain things (either Torchic, Mudkip, or Treecko).
No, you can not catch Phanpy in SoulSilver. It is a version exclusive to HeartGold.
You cannot catch Heatran in Pokémon SoulSilver, you will have to trade for it.
You cannot catch Celebi in Pokemon Soulsilver, you have to transfer it from Diamond and Pearl (if you have it in those games).
you trade
No.
No.
You can use any type of Poke Ball that you want to catch Spheal in Pokemon SoulSilver.