How to get Gold, Silver, Crystal pokemon in Yellow.
1) Beat the Elite 4, 4 times.
2) Do the MissingNo trick and capture him.
3) Beat the Elite 4 again, then look at your hall of fame.
4) If this picture appears, go on, if it doesn't, repeat steps 1-3.
5) Go into Prof. Oak's lab, and talk to Prof. Oak. The picture below should happen.
6) Reset your game, and goto his lab.
7) He should say this :
8) Goto the 2nd bookcase, and click on it.
8) You should have the GS ball.
9) Goto any piece of grass, and use the GS ball.
10) Battle your Gold, Silver, Crystal Pokemon, and capture it!