It's impossible to catch one without cheats.
You must get the purified croconaw from Pokemon colosseum or a totadile from Pokemon emerald or one from Pokemon xd gale of darkness then trade it to firered if you have the croconaw you just need to breed it to get totadile.
A lure ball :)
Technically Cyndiquil is the strongest but it all depends on what type of Pokemon you want.
No, you cannot catch Kyogre in "Pokémon SoulSilver."
You can't catch bastiodon in Pokemon soulsilver.
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.
use the poke radar in route 224 warning you must have mystery gift
catch it? no.
there's no possible way to catch mew in the game. you have to go to an event in REAL LIFE to get it or from wi-fi if you've already seen it.
Yes, you can keep on attempting to catch Entei provided you keep on defeating it. Every time you defeat Entei in Pokémon SoulSilver, you can beat Lance and Entei will respawn.
If you go to the Ilex Forest on a certain day in the summer, there is a celebration I think for Celebi which is when celebi will appear. You can catch it then.