No, it cannot be encountered again after it has been caught.
If you cant im never playing Pokemon again
you can go back and beat him again the next day!
At lv. 30 and again at lv. 50 or 55, depends on how you raise it's level.
Yes trainers can rematch you in Pokemon crystal but you must register there phone numbers to do that but not all trainers will rematch you, wait until the trainers call you they will mention they want to battle again and they will remind you where they are go there and talk to the trainer to battle them again. They can keep calling you for rematches throughout the game don't miss the chance to rematch them.
Route 9, they swarm every now and again
you have to get the badge in golden rod city just talk to the gym leader again
Just go to Slowpoke well and save, so when you go in the game again you will enter slowpoke well.
You cannot get the Liberty Pass again. It was an exclusive thing that nintendo will not release again.
That was just a Mirage of the Pokemon Darkrai. You won't be able to see him again though but you can go into that inn any time after fighting/capturing Darkrai!
it seems that you have to beat wintley again without the cheat.. i had the same problem but i ve tried again without celebi and did it..
A Red Gyrados is just a Shiny Gyrados. Theres a 0.5% chance that you'll run into a shiny Pokemon, or the PokeRadar can eventually find one by creating a chain of finding and either capturing or defeating the same Pokemon over and over again. If you run, that will break the chain. However, in Pokemon Gold, Silver and Crystal (as well as Heartgold and Soulsilver) just surf to the center of the lake of rage (north of mahogany town) and you will find a red gyrados.
I don't know if you can get it in crystal, but i know you can get it in Gold and Silver versions. So you go to Union Cave. then you take a secret path (involves surf) and you go to this small patch of grass. In there you can find Smeargle (I think that's how you spell it) and Natu. Again i'm not sure if you can find them in crystal.