Do you think it's possible to defeat Soul Silver with just one pokemon?

Yes it's possible. i personally have done it. i chose Cyndaquil and only used him and was able to beat the entire game. however if you are going to attempt such a thing make sure u have plenty of potions and revives. especially for the Elite 4

I don't think it's possible to go through the game with just one pokemon. You can't get to the move deleter until you get to Blackthorn City, a pokemon can only have 4 moves at a time, and there are only two pokemon that can learn every HM: Mew and Arceus. And it wouldn't be fair for battling, since you'd have to trade both and they wouldn't be at a low level when you start.

Unless, of course, you mean only using one pokemon for battling and having others for HMs, in which case it's definitely possible. Hard, but possible.

I beat pokemon Blue with nothing but a level 100 Mew.

It depends---- What do you mean by 'defeat'?

There are several objects to Pokemon; to fill your pokedex, to become stronger as a trainer, to collect your favorite pokemon or rare pokemon, or to simply beat all the trainers inside the game.

You could win battles, but it's best to have at least one other pokemon, so that if your first one faints you have another to send out while you revive the other. If you do try to use only one, better go with a legendary, preferably level 100, or at least level 90.

With Typhlosion, no problem. I personally have lots of patience and just grind-train on low level wild pokemon (for both evs and levels) usually by the time I get through the first region the main pokemon I am using will be at least level 75 or 80.

yes its possible but it would take one hell of a beefed up pokemon to do it, and i might attempted to but i don't know if i would ever have the time to make a pokemon that strong

no its not because of the HM thing

never played it