15 and then you have to realise that you suck at Pokemon and should give it up!
You cannot catch Thundurus in Pokemon Black, he is exclusive to Pokemon White.
Only once. Ho-ho and the other Pokemon in the Whirl Island.
No because the man who teaches you how to catch Pokemon will not show you how to catch Pokemon no matter how many times you talk to him plus if he does show you how to catch Pokemon and you go to cinnibar island and try to find missingno it still will not show up ever.
Well if you mean admins like Ein you have to battle so many times in the deep colosseum. For Ein i THINK you have to battle and win 4-3 times
you can catch as many legendary Pokemon but only once unless you have it on the computer
no.
There are many Pokemon you catch that are similar in sapphire and emerald but there are many Pokemon emerald can only get and not sapphire.
I don't now but I believe that you can catch as many as you want when you encounter them.
Once! Just press L while your walking in grass! (or both L and R)
Yes you can it might be difficult but try many times any you will eventually catch one. you cannot use any moves though.
Start by getting a lot of pokemon balls and then catch as many Pokemon as you can. Just catch Pokemon till you get to 200.
Yes, just catch one and tap it over 100 times, it will appear as a legendary pokemon.